—Ishamael to Lews Therin Telamon
Ishamael (ih-SHAH-may-EHL; /ɪˈʃɑ.mɛɪˌɛɫ/; Old Tongue: Betrayer of Hope), previously known as Elan Morin Tedronai, was the most powerful of the Forsaken and their de facto leader during the War of Power. Later, he was officially granted the title of Nae'blis and given direct authority over all of the Dark One's other followers.
He was a handsome man in his middle years, with dark eyes and cruel looking lips. He had mellifluous voice. 
In "The Wheel of Time Companion" his level of strength in the One Power is ++1, putting him above all other channelers except Rand al'Thor and Rahvin. He was said to have been the only person who matched Lews Therin in power.
Age of Legends
Elan Morin Tedronai was a critically acclaimed philosopher and theologian who wrote several influential books, among them Analysis of Perceived Meaning, Reality and the Absence of Meaning and The Disassembly of Reason. Despite his acclaim however, his writings and philosophies were often considered too esoteric for popular appeal.
At some point, a group of Aes Sedai researchers drilled the Bore into the Dark One's prison, and caused the Collapse. Once it became known just what it was that those researchers had unleashed, Elan put forth a theory that the war between the soul of Lews Therin and the Dark One had occurred since the beginning of time, recurring at intervals along the Wheel of Time. This theory led him to realize that, due to the Wheel's cyclical nature, the Dark One would invariably receive an infinite number of chances to escape from his prison. As such, he realized that humanity would have to continually fend the Dark One off so long as the Pattern existed, and that each victory by humanity simply led to another battle. The Dark One, on the other hand, needed to win only once, as once he did, that victory would be absolute as it would be impossible for humanity to combat him once freed from his prison. He also realized that because the Dark One had a theoretically infinite number of chances to win, it became a statistical certainty that he eventually would. However, he failed to realize that every version of the battIe between the light and the shadow has already been fought throughout the ages and that the Dark One had never been able to escape his prison. In accordance with his belief that the Dark One's victory was inevitable, he became one of the first Aes Sedai in the Age of Legends to publicly declare himself for the Shadow. He announced his betrayal at a conference of Aes Sedai in the Hall of Servants, informing them of what it was they faced. His announcement sparked massive riots. He was given the name Ishamael by the people: Betrayer of Hope. After his conversion to the Shadow, he came to believe that he himself was part of the eternal conflict between the Dragon and the Dark One, serving throughout the ages as the Dark One's champion. Despite the fact that he appears to be the only human being with the same strength in the One Power as the Dragon, it is not known whether there is any truth to his belief. It has been confirmed however that his soul and that of the Dragon are often spun into the Pattern together.
During the subsequent War of Power, he became the Dark One's greatest champion and the only Forsaken equal to Lews Therin in the One Power. At some point during the war, he was named Chief Captain-General of the Shadow, despite the fact that he never held a field command. This title gave him supreme command over the forces of the Shadow and made him the de-facto leader of the Forsaken. He was defeated in some capacity by Lews Therin at the gates of Paaran Disen, and he was humbled at some point by Lews Therin in the Hall of Servants, though it is not known if either event occurred during the war as Ishamael never personally directed any battles.
When the Dark One's prison was sealed, it is thought that Ishamael was only partially sealed behind it (in contrast to Aginor and Balthamel who were merely sealed too close to the edge, and thus susceptible to the passage of time). What is known for certain is that his soul was spun out of the Dark One's prison and into the Pattern from time to time after the prison was sealed. In fact, Ishamael may not have been initially bound at all, since he visited Lews Therin Telamon (apparently in person) after the seals on the Dark One's prison had been placed (as Ishamael spoke of the sealing in past tense, and Lews Therin was already mad).
After the seals were placed and saidin was tainted, Ishamael arrived at Lews Therin's home and discovered to his surprise and delight that Lews Therin had murdered his entire family. After having a mostly one-sided conversation with the insane Lews Therin, Ishamael Healed him so that he understood what he had done. This realization caused Lews Therin to commit suicide, leaving a furious Ishamael to wait for him to be reborn.
Aran son of Malan son of Senar (born roughly 50 AB) had a theory based on Ishamael being thrown out and touching the world for specific periods of time. Aran had heard claims that people had encountered him as long as forty years after the sealing of the Bore. Using lost manuscripts, Aran concluded it might have taken some time for Ishamael to be brought into the prison with the remainder of the Forsaken, and might possibly have been "thrown out" in a regular cycle. There is ample evidence to now support this hypothesis such as interviews from Darkfriends saying that as early as 983 NE they were receiving instructions from someone calling himself Ba'alzamon. It's possible the cycle lasts a thousand years, as the Trolloc Wars, War of the Hundred Years and the events of the current time are all a thousand years apart and Ishamael is known to have played a significant part in all of them. Ultimately, it appears as though, once every thousand years, Ishamael was released from the Dark One's prison for forty year intervals, and he played a key role in destabilizing human civilization each time he was released.
Possibly due to his own madness, Ishamael started calling himself Ba'alzamon ("Heart of the Dark" in the Trolloc tongue). He was revered by Trollocs, feared by Myrddraal, and widely believed to be the Dark One himself. His first period of liberty from the Dark One's prison occurred right in the middle of the Trolloc Wars, at a time when humanity had begun to hold its own against the Trolloc hordes. His presence re-invigorated the Trolloc armies and gave them direction. His most devastating action during the Wars was when he led the Shadows forces in directly assaulting Manetheren. The attack destroyed Manetheren and allowed the Trolloc armies to ravage nearly all of the Westlands. However, Ishamael disappeared abruptly after forty years, depriving the Shadow of his leadership and allowing forces under the command of Rashima Kerenmosa to push back and ultimately defeat the Trollocs.
In FY 973, Ishamael came to Artur Hawkwing's court as Jalwin Moerad. He became Hawkwing's highest counselor by summer FY 974, and held that position until Hawkwing's death in FY 994. He set about wrecking that which Hawkwing had built, advising him to dismiss all Aes Sedai from his service, lay siege to Tar Valon, send his armies across the Aryth Ocean, and refuse Healing on his deathbed.
Jalwin Moerad had a volatile temper, and was believed to be half mad. He was frequently absent for long periods (which led Tamika, Artur's wife, to distrust him) and anyone who inquired about him closely died. He was also openly contemptuous of Aes Sedai. Days after Artur's death, he became counselor to, and then ordered killed, the three closest contenders for the throne (Marithelle Camaelaine, Norodim Nosokawa, and then Elfraed Guitama), one after another. Then, forty years after his appearance, Moerad disappeared, having never aged a day. In his wake however, he left a fragmented number of fiefdoms that had been carved out of Hawkwing's empire, which solidified into individual nations and prevented humanity from forming a unified government.
Ishamael's final cycle of freedom occurred as the seals on the Dark One's prison were weakening, resulting in him being permanently released from the Dark One's prison in 997 NE. At some point before the other Forsaken were released, he was informed by the Black Ajah that the Dragon had been reborn. By that time, his overuse of the True Power, possibly combined with his cycles of being thrown out of the Bore, had driven Ishamael completely insane. His dependance on the True Power had also warped his body to the point where his eyes and mouth were occasionally replaced by what appeared to be endless caverns of fire, though he maintained his original appearance in all other ways. Learning of the Dragon's rebirth, he used Padan Fain to locate Rand al'Thor, hoping to come across the Dragon Reborn before he could become dangerous. He hunted Rand relentlessly through his dreams (he also pursued Matrim Cauthon and Perrin Aybara until he was certain Rand was the Dragon Reborn), attempting to turn him to the Shadow. Rand finally confronted him at the Eye of the World in a Dreamshard of Ishamael's own making. There, he drew upon the Power in the Eye and severely burned Ishamael, though he did not manage to do any lasting damage. Once he had sufficiently recovered, Ishamael began his pursuit again, culminating in a duel between himself and Rand at Falme. Through unknown means, he and Rand appeared in the sky above Falme as they dueled, visible to anyone near the city. It is theorized that the borders between the worlds fracture whenever the light confronts the shadow. The place of the duel bears some resemblance to the darkness between Tel'Aran'Riod and the dreams/dreamshards of the Forsaken that Perrin and Hopper visit, indicating that Rand and Elan fight either in Tel'Aran'Rhiod or yet another dreamshard. During the Last Battle, another example of a clash between the light and the shadow, Rand and those with him are able to interact with Perrin who is in the World of Dreams. We don't know what causes the walls between the real world and the Wolf Dream to crumble. (The evidence points against this being a frequent event but does not rule it out entirely.) Ultimately, Rand managed to wound Ishamael with his Power-wrought sword, which melted from the heat of Ishamael's body when it struck him. However, Rand received a far more grievous wound in return, as Ishamael struck him in the side with a quarterstaff,. wounded him with an incurable wound which at the end fulfills the following prophecies:
"The Reborn One, marked and bleeding"
"Red on black, the Dragon’s blood stains the rock of Shayol Ghul.
In the Pit of Doom shall his blood free men from the Shadow.
His blood on the rocks of Shayol Ghul,
washing away the Shadow, sacrifice for man’s salvation."
Rand receives no bleeding wound from his fight with Moridin but his old wound on his left side opens and bleeds during the fight.
His third and final confrontation with Rand occured a few months later in the Heart of the Stone of Tear. There, Rand managed to acquire the sa'angreal sword Callandor, and with it, was able to overwhelm Ishamael's own power. During the end of their battle, Ishamael called directly upon the Dark One to aid him, and was implied to have drawn in so much of the True Power that he could have matched even Callandor. However, before he could use this power to attack Rand, he was impaled by Callandor through the heart and slain. It was noted afterwards that his body decayed to dust almost immediately after his death, likely due to it having been ravaged by Ishamael's use of the True Power.
Talents and Personality
—Rand al'Thor to Moridin
Ishamael was incredibly intelligent, and had profound insight into the nature of the Wheel of Time and the struggle between the Dark One and the Dragon. Before the War of Power, he had been a philosopher and theologian of great renown, and was noted for his extraordinarily logical demeanor and way of thinking. He was unique among the Forsaken in that he was the only member of the group who did not join for the promise of power or immortality (at least not per se), but because his logic concluded that the Dark One must inevitably win against the Dragon, and therefore the only path was to join him and rule for a time. All of the other Forsaken believed him to be insane, though some of Ishamael's statements, which were taken to be mad, were in fact simply esoteric beyond what the other Forsaken were capable of understanding (his brief talk on Chaos Theory for example). However, by the time of the Third Age, he was in fact completely mad, and may have even believed that he himself was the Dark One at times. He was also fairly disdainful of the other Forsaken, regarding them all as fools for not understanding the nature of the Dark One, and for believing that he would hold to his promise of giving them power and immortality. As Ishamael, he appeared to desire power and recognition, both of which he achieved in spades as the Dark One's most favored disciple. This went hand in hand with a desire to demonstrate how pointless he believed fighting against the Dark One was. He also appeared, as numerous other Forsaken were, to have had a desire to prove himself greater than Lews Therin. However, his desire seemed to be at least partially rooted in his idea that he and Lews Therin were each the respective champions of the Dark and the Light, and that they were destined to always battle each other so long as the Wheel turned. He also was noted by Moghedien as having had a sadistic streak, at least when it came to watching his rivals suffer. As Ishamael, he was once described by Sammael as having been "more than half mad, and less than half human."
When he was later re-incarnated as Moridin, his personality changed drastically. Though his madness was said to have been even greater as Moridin than as Ishamael, he exhibited a preternatural calm most of the time, and appeared to have left both his pride and his desire for power behind him. Additionally, he lost any hint of sadism that he had once had, and took more often than not to simply brooding in silence. Instead, he seemed fatalistically devoted to seeing the Dark One triumph, as he believed that his service to the Dark One would grant him his truest desire; to die so completely that he would never have to be reborn again. This desire was brought on by an overwhelming sense of self-loathing, and utter despair regarding what he saw as the inevitability of the Dark One's victory. This desire was apparently so strong that, rather than being punished (both for dying and for impersonating the Dark One) upon resurrection like the other re-incarnated Forsaken, the Dark One deemed that returning Ishamael to life in and of itself was punishment enough. His insanity, therefore, took on an omnicidal tone rather than a power-mad one, as the only thing he wanted was to bring about a permanent end to the world as quickly as possible. However, he did appear to suffer from violent mood swings at times, thought they were very, very transient and he tended to regain control very quickly. Several comments from Graendal suggested that, before his conversion to the Shadow, he may have been much like Rand al'Thor. Indeed, the two of them, even as mortal enemies, appeared to get along oddly well during their numerous conversations in Dreamshards, and before re-integrating Lews Therin's memories with his own and recovering, Rand nearly destroyed the Pattern in a nihilistic despair similar to Ishamael's own.
Ultimately however, despite understanding a great deal about the nature of the Pattern, he ultimately failed to realize the true nature of the Dark One, having believed that the Dark One would have allowed him the peace of oblivion despite the fact that the Dark One was completely incapable of granting peace or rest of any sort.
Apart from being one of the most powerful male channelers - as strong as Lews Therin Telamon - Elan Morin Tedronai was also one of only a few male Dreamwalkers. He used this talent extensively, communicating his orders to Darkfriends via their dreams. He trapped many Darkfriends in Dreamshards to punish their failures, and he also used tel'aran'rhiod to lure the three ta'veren. He also spent much of his leisure time in very subtly twisted Dreamshards. His favorite settings appeared to be realistic places that contained warped or impossible elements. His typical setting involved sitting alone in front of a fireplace that radiated no heat, with disturbingly human-shaped flames and clouds bursting and contorting, and burning rats behind the fireplace. Others involved places like a platform floating on endless water with people chained under the waves, perpetually drowning and being eaten by giant, unseen predators.
Moridin was able to access the True Power, the Dark One's version of the One Power. He was capable of channeling far, far more of it than he could of the One Power, due to his position as the Dark One's favorite Forsaken, and used it to the exclusion of the One Power. This ultimately caused him numerous problems, such as increased insanity, but due to him already being insane, these effects were blunted somewhat, and though he was mad, he was still more than capable of functioning even as Ishamael. His overuse of the True Power also occasionally caused his eyes and mouth to appear as bottomless caverns of flame when his emotions spiked, though this effect ceased when he was resurrected.
He was able to use the True Power to detect both saidar and saidin.
Parallels and trivia
Ishamael's alias, Ba'alzamon, may be a reference to and combination of Beelzebub, one of the seven princes of Hell, and Ba'al, also one of the seven princes of Hell as well as a name given to several Demons in Christian mythology. Ba'alzamon may also be a reference to the Carthaginian supreme god Ba'al Hamon.
The name Moridin may be an allusion to Mordred, the bastard son and patricide of King Arthur.
Ishamael is master of the board game sha'rah.
As Moridin, it appears that he can hear the commands of the Dark One without being at Shayol Ghul. This may not be unique however, as it would seem that Ishamael as Ba'alzamon could communicate with the Dark One in a similar fashion; he appeared to beseech the Dark One for aid in combating Callandor, and he apparently received it. This ability may be connected to his overuse of the True Power.
Ishamael appears to be something of a nihilist, considering his belief in the futility of mankind's struggle against the Dark One and the titles of his books. However, believing there is no hope is not the same as having no belief at all, a common misconception. A nihilist being anarchic, takes away the 'means' to any 'end'(through/from their own perspective) to them-self; namely goalless and chaos seeking.
When channeling, Ishamael appears to use the True Power almost exclusively, despite having the maximum possible level of access to the One Power that a human can achieve unaided. He does this despite the fact that the True Power is said to drive its wielders insane after a time, and how incredibly dangerous it is to use. However, Moridin, being insane already, seems to have no difficulty in either wielding it or combatting its incredibly addictive nature.
It is also noteworthy that his name, Moridin, means "death" in the Old Tongue, and given the Dark One's twisted sense of humor in naming his resurrected followers, renaming Ishamael as Moridin may have been an ironic joke on the part of the Dark One.
An unofficial soundtrack has been released, based on Rand's first encounter with Ba'alzamon in his dreams. Follow the link to listen on YouTube.