The Dark One is a primordial, sentient, cosmic force of evil in the universe. The Dark One's goal is to break the spirits and hearts of whatever sentient beings he can influence, and, if freed from his prison, eventually to remake Creation in his own image. His actions appear to indicate that he is also a force of chaos, destruction, and discord, as many of his underlings, as well as Shaidar Haran, seemed to place a great deal of emphasis on increasing the amount of chaos in the world at any opportunity. His existence is revealed to be an integral part of human free will, as his malign influence encourages humanity to make selfish choices. If destroyed, humans (and likely other sentient beings) would possibly become completely incapable of evil, violence, or selfishness in any respect. He is said to have been imprisoned by the Creator at the beginning of time in a separate dimension outside of normal reality, and outside of the Pattern, and has sought ever since to break free of his prison and destroy the Wheel of Time and remake the world according to his image and purpose, or alternatively, to destroy creation completely. He is currently imprisoned, outside of the Pattern.
His true name is Shai'tan, (pronounced: SHAY-ih-TAN), although many people believe that speaking that name will bring misfortune to the speaker, which is why he is referred to as the Dark One. However, there are many other alternative names for him, such as:
- Father of Lies
- Sightblinder (used by the Aiel)
- Lord of the Grave
- Lord of the Twilight
- Shepherd of the Night's flocks
- Heartfang (used by the wolves)
- Old Grim
- Leafblighter (used by the Aiel)
- Father of Storms (used by the Atha'an Miere)
- Caisen Hob ("Old Hob", used by people from Shandalle and the Seanchan)
- Lighteater (used by the Seanchan)
- Soulblinder (used by the Seanchan)
- Great Lord of the Dark (or simply 'the Great Lord')
- Lord of the Grave
- Lord of the Evening - a name used in the Prophecies of the Shadow
The name Ba'alzamon (meaning "Heart of the Dark" in the Trolloc language) was used by Ishamael before his death; humans, including Darkfriends, learned it and assumed that it was the Trolloc name for the Dark One, which led to the assumption for the duration of the first three books and for much of the world's history that Ishamael was actually the Dark One himself - a falsehood which he did nothing to repudiate, and in fact encouraged the misconception, choosing his words carefully, so as not to actually claim to be the Dark One.
In the Age of Legends Aes Sedai research scientists, including Mierin Eronaile and Beidomon, believed they have discovered a new source of Power, one which can be used by both men and women. What they were discovering was the prison of the Dark One and drilling into it they have created the Bore, partially freeing the Dark One, as he was able to touch and influence the world. The moment of the drilling is described in one of the visions of Rand al'Thor in Rhuidean in the Aiel Waste. While he walked through the glass columns ter'angreal, he learned and experienced the history of the Aiel, seeing and living moments of it through his ancestors' eyes.  There Rand also learns of a time when the Dark One held no sway and there were no shadowspawn nor armies in the past as said in The Shadow Rising, “The Dark One had been bound away and no one knew his name nor the word ‘war.’”
When encountered by Rand during the final assault on Shayol Ghul, the Dark One is described as being powerful beyond measure; a universe-spanning force of evil that is both incomprehensible in its nature and infinite in its being. His presence is described as being beyond space, size, and time, and his essence is said to be utterly empty, yet infinite. Though the Dark One is beyond the concept of time, he is constrained by it in his interactions with the Pattern simply because it is an integral part of reality. The situation is described as being akin to an artist's imagination exceeding the limits of the material they have to work with. It is for this reason that he cannot retrieve people's souls that have been burned from the Pattern by balefire. Time does not exist for the Dark One, but since it does exist for a person's soul, he is unable to reach outside of time itself to touch souls burned from the pattern. However, the Dark One can retrieve souls that die by virtually any other means, and transmigrate them into new bodies. However, he has only been known to do this with individuals who have pledged their souls to him, such as the Forsaken, which indicates that he has less power to manipulate souls not pledged to him. Other than balefire, being consumed by Mashadar may also place a soul beyond his reach, as Mashadar is implied to have the ability to devour souls, and Sammael was never reborn after being killed in this manner. However, no direct evidence is given beyond Sammael's death to validate this, as the Dark One seems to have decided that some souls are not worth bringing back, including some Forsaken, such as Aginor after his second death by conventional means. The Dark One is also unable to give people the ability to channel the One Power, or to change the amount of the One Power that a channeler can draw.
Verin Sedai has noted the Dark One is the "embodiment of paradox and chaos, destroyer of reason and logic, breaker of balance, the unmaker of order". She also states that, while she believes she understands the Forsaken, she has no idea what the Dark One's goal is, what he wants, or even what he is. Moridin has stated that the Dark One's eventual goal will not be to destroy reality and remake it, but rather to simply destroy everything. However, the Dark One's goal is later revealed to be remake the pattern in his own image, although he would be content to destroy creation, giving Moridin the oblivion he craves. He has no specific preference as to how the world would exist after his victory, as long as no one other than himself is in control. To Rand al'Thor, he presents various possibilities, from a completely tortured, ruined world and people, to a world in which he has simply removed the capacity for people to feel compassion or empathy for each other. The only constant with regards to his desire to remake the world is an emphasis on his own prominence in that world, whether the world's population is aware of it or not (one of the most common things he says to Rand al'Thor when describing how would change reality is, "THERE IS ONLY ME"). The concept of simply destroying creation however, is also stated to be something that he would be satisfied with. The Dark One seems to have a sense of humor, laughing at the end of The Lord of Chaos after hearing Demandred's unknown news. Because he wishes to break his foes, destroying them is not necessarily part of his plans. To that end, he often ordered that none of his followers were to attempt to kill Rand al'Thor before he could reach the Last Battle (though many of them flouted this command). His strategy seems to be to turn the Dragon Reborn to the Shadow, which would give him the best hope of defeating the Light. Although destroying the Dragon Reborn always seems to be a close secondary plan. As a cosmic embodiment and source of evil, he is completely incapable of understanding concepts like nobility and compassion, and is also evidently incapable of performing or experiencing anything that could be considered good. Additionally, despite his vast, cosmic knowledge, and his innumerable contingency plans, he appears to be incapable of learning from past mistakes, having failed to defeat the Light throughout many ages past. He appears to lack the understanding necessary to succeed.
The Dark One is capable of warping reality to certain degrees within the Pattern without being able to actually touch it, so long as his prison is not completely sealed. Around and within the area of Shayol Ghul, he is capable of changing the height of the stalactites on the ceiling of the tunnel that leads to the Pit of Doom without actually seeming to make them move. He can also warp distances and perceptions within Shayol Ghul. How he does this is not known, but Rand al'Thor demonstrated the ability to counter this meddling through force of will combined with his ta'veren nature. Additionally, the lands around Shayol Ghul, at least those lands that aren't completely devoid of life, are filled with unnaturally deadly creatures and plant life, much of which is in an accelerated state of decay. If one is actually within the Pit of Doom, one can hear the Dark One's "voice", as it were, as a telepathic projection of immense power. With the possible exception of Ishamael/Moridin, the Dark One is not capable of directly communicating with anyone in the Pattern unless they are present at the Pit of Doom. Why Moridin seems to be exempt from this may be due to his continual, high level use of the True Power. The Dark One's ability to manipulate the Pattern has grown as the patch over the Bore has weakened. This has been the cause of numerous destructive, chaotic events that seem to occur at random over time, but increase in frequency as the seals weaken;
- The Forsaken began to escape, starting with Aginor and Balthamel.
- Bubbles of evil, likened by Moiraine to a miasma in a swamp, emanate periodically from the Dark One, twisting reality in the Pattern to lethal effect, especially near ta'veren.
- The Dark One often uses the environment against his enemies. In The Eye of the World, he attempted to cause widespread starvation through prolonged winter. The unnatural winter was broken by Rand al'Thor, as he unintentionally uses the store of pure saidin at the Eye of the World. He also causes unnatural heat but this is also stopped by Elayne and Nynaeve when they use the Bowl of the Winds. Currently, the world is shrouded in perpetually overcast skies, but it is unknown if the Dark One is responsible for this most recent abnormal weather.
- Images of the dead/ghosts have begun to appear as the Last Battle approaches.
- The world in general dying and decaying; plants going into hibernation-like, death-like states, food spoiling, animals hibernating, etc.
The Dark One is the source of the True Power, which is analogous to the One Power. However, one can only draw on the True Power with the Dark One's blessing. Use of the True Power creates saa; little flecks of black that move horizontally across the eyes of the wielder. Furthermore, it is much more addictive than either saidin or saidar, and it is believed that not even the strongest willpower can fight the desire to use it once the saa have begun to manifest. The more a channeler uses the True Power, the more saa are seen. Saa doesn't affect the channeler's vision. The True Power is demonstrated to be centered around death and destruction; for example Moridin uses it accidentally to crush the life out of a servant. It is also highly destructive to its user, the saa will eventually turn the user's eyes completely black, at which point caverns of fire may manifest at times where the mouth and eyes of the channeler would be. This is a highly advanced stage of True Power usage and the user will die soon after unless they have been granted immortality by the Dark One. This power is given to only the Dark One's most favored servants, and in quantities reflecting the particular individual's favor. Rand al'Thor later discovers the ability to access the True Power by means of a link that he and Moridin accidentally created between their souls. Using Callandor, it is possible to use the True Power against the Dark One himself, as it is a True Power sa'angreal, and the Dark One can't immediately cut off access to the True Power if one is wielding it in such large quantities as Moridin could while wielding Callandor.
Despite his cosmic levels of power, it is possible to kill the Dark One by bringing him into the Pattern. This is due to the fact that time exists within the Pattern, and as such, things can be brought to an end within the Pattern. Rand al'Thor managed to accomplish this by using the One Power in addition to the True Power; the Dark One's own energy. Ultimately however, in light of his knowledge of the Dark One's impact on human free will, he chose to simply seal the Dark One back up again. Additionally, so long as his prison is completely intact, the Dark One apparently cannot breach it without outside aid. However, he can chisel away at existing holes to further widen them.
While the Dark One appears to be the source of all evil with regard to the choices of sentient beings, there are evils that exist that have nothing to do with the Dark One, and can even be seen as being in opposition to him. The most prominent example of this is the being that eventually became known as Shaisam, who was noted to want to kill the Dark One if it had had an opportunity to do so.
The name Shai'tan is likely taken from Satan the Hebrew word for the adversary, later translated to Shaitan, or Sheytaan, the Arabic word usually referring to "devil". The name Ba'alzamon is also taken from the Old Testsment Hebrew Bible where the name for the pagan god Baal and the pagan god of the Philistines is Beelzebub, in Hebrew written Ba'al Zəbûb, 2 Kings 1:1–18 and in the Greek Christian New Testament it is applied to Satan the Devil at Matthew 12:25-28 and in other verses.
Possible Cosmological Function (speculative)
The purpose of the Creator in bringing the Dark One into being is an issue that is occasionally pondered by a few of the characters in the series, due mostly to the widely perceived idea that the Dark One seems to serve no obviously functional purpose in the grand scheme of Creation. He appears only to exist to cause misery and suffering that seems not to be countered by any direct influence from the Creator. However, it is shown by Rand al'Thor during his metaphysical conflict with the Dark One during the Last Battle that the Dark One functions as the sole enabler of any sentient tendency towards selfish behavior of any kind. Given that fact, and given the fact that the Creator seems to have at least some interest in safeguarding his Creation (assuming that the disembodied, telepathic "voice" that Rand heard twice outside of Shayol Ghul was in fact the Creator), it is possible that the Creator made the Dark One specifically for the purpose of allowing his creation to have free will.
It is also commonly believed that the Dark One' prison being breached by humanity is a cyclical, inevitable part of the Wheel of Time and the Pattern. Ishamael in particular, who was an extremely accomplished philosopher and theologian, believed that the Wheel of Time continually provided the Dark One with opportunities to be freed throughout history because of the Pattern's requirement for balance. However, particularly given the extra-realistic nature of the Dark One, there is evidence to suggest that the cyclical inevitability of this event might be wrong, or at least might not be nearly as regular an event as Ishamael believed it to be.
After Rand sealed the Bore permanently, he came to realize that the havoc that the Dark One was able to wreak on the world was ultimately all facilitated, enabled, and carried out by human beings; that the Dark One was, ultimately, not the true enemy in the sense that humanity's collective suffering is always entirely due to the decisions of individual humans. With regard to human behavior, the Dark One ultimately had no more power inside the Pattern, even with the presence of the Bore, than humanity allowed him to have. Despite his utterly malicious nature and his cosmic levels of power, he was not directly responsible causing any of the problems attributed to him; he could not destroy humanity without the cooperation of humanity itself. As to the more direct influence of the Dark One through the Bore, the balance of the Pattern was shown to intrinsically counter the extra-realistic meddling of the Dark One through various mechanisms. Additionally, the negative elements of the world that the Pattern might require to balance itself can be seen to insert themselves into reality without requiring any direct influence from the Dark One. For instance, Rand believed that because the world government during the Age of Legends seemed unwilling to admit that the "utopian" society of the time had a considerable number of social problems, and that a societal collapse of one kind or another may have been inevitable even without the drilling of the Bore. Such a collapse and descent into war would have provided the disastrous destruction necessary to balance out the achievement of the Age of Legends without requiring the Dark One's prison to be breached. Also, as the Dark One exists outside of the Pattern, his direct influence may not be considered to be a part of the "balance" that the Pattern inevitably weaves into itself. What is more, the Dark One is completely incapable of learning from past mistakes due to his inability to understand anything good, and he cannot break out of his prison without help from humanity itself. As such, if the breaching of the Dark One's prison is indeed inevitably cyclical in nature and seemingly brought about by human choice, there would be no reason to assume that the re-sealing of his prison time and again is any different. This is highlighted when Rand brings the Dark One physically into the pattern and the beings true form is so small and weak that Rand can pinch him between his fingers, with Rand even condescendingly calling him a mite.