Isam waited in the high passes.
The hunt is now begun. The Shadow's hounds now course, and kill.
One did live, and one did die, but both are."
—Excerpt of the Dark Prophecy
The being known as Slayer is the merger of the two souls of Isam Mandragoran and Luc Mantear. Little is known about this dark creature or his origins.
He looks very similar to Lan. He is tall and muscular with thick arms. He is tanned with dark hair and blue eyes which appear black in tel'aran'rhiod.  Perrin Aybara comments that his scent smells inhuman, like a man mixed with stone.
When Malkier was overrun by Trollocs, Isam was one of the few Malkieri to escape. His mother Breyan Mandragoran fled with him into the blight, but they were attacked by Trollocs. Isam survived this encounter and as a child, grew up in the Town. There he lived a very dangerous life, where each day was a struggle to survive surrounded by Samma N'Sei and Myrddraal. He learned to kill very early and this upbringing is what has honed him into the hunter he is today.
EWoT:Luc was the First Prince of Andor and brother of Tigraine Mantear, making him the blood uncle of Rand al'Thor and Galad Damodred, both sons of Tigraine.
He is tall and broad shouldered, with dark red hair, with white wings at the sides.
Gitara Moroso, at that time the advisor to Queen Mordrellen Mantear of Andor, later on Keeper of the Chronicles under the Amyrlin Seat Tamra Ospenya, an Aes Sedai of the Blue Ajah who possessed the Talent of Foretelling, urged him to seek his glory in the Blight. It is speculated by many fans that this is where Luc and Isam met. Somehow, both of them survived in the Blight. They met in the Mountains of Dhoom and merged into something new.
After Tigraine died giving birth to Rand, Janduin could not forgive himself and went into the blight hunting Trollocs and Myrddraal. It was said he was killed by a man who looked like Tigraine, possibly Slayer (in the Luc Mantear form).
Slayer has many abilities. He can appear in both forms in the world of flesh, but he is also a master of the World of Dreams and can change easily there as well. In fact it is in Tel'aran'rhiod that Slayer was given his name by the wolves, due to his propensity for killing their number on sight. He often appears as Luc in the waking world, and Isam in Tel'aran'rhiod, but there are exceptions. He can also enter the Tower of Ghenjei. It seems that both Luc and Isam's personalities have survived intact, and that Luc is just as evil as Isam. In fact, they seem to get along with each other.
Cleaning up loose ends
Perrin first encounters Slayer in the Wolf Dream. He finds that Slayer killed a wolf and chases him to the Tower of Ghenjei.
Perrin meets Lord Luc in the Two Rivers. He calls himself a Hunter of the Horn, trying to help the Two Rivers people. He recognizes Perrin when they first meet even though Perrin has never met "Luc" before. He constantly undermines Perrin's orders. He arranges a trap for Perrin's group that is hunting Trollocs. Perrin confronts Slayer in Tel'aran'rhiod and defeats him. In the waking world Luc also has been wounded and flees from Emond's Field. He attempted to kill Padan Fain in the Two Rivers, but was unsuccessful, and he both fears and hates Perrin.
He continued hunting Ordeith, and later tried to kill Rand and Min Farshaw. It was he who mysteriously chose to eliminate the Gray Man who tried to kill Egwene al'Vere in the White Tower. He also killed the Black Ajah sisters Amico Nagoyin and Joiya Byir, who were being held in the Stone of Tear.
Rand remained completely unaware of Slayer's nature and relation to him. Birgitte states that he is a new occurrence, but perhaps an old evil. As Luc, he is spotted by Egwene, Elayne Trakand and Nynaeve al'Meara while spying on them in Tel'aran'rhiod. Later when again Nynaeve is in Tel'aran'rhiod, she is shot at by a man who looks very similar to Lan, probably Isam.
Confrontation with Perrin
Slayer is shown to be under the command of Moridin. Moridin lends Graendal the services of "the one with two souls" in order to kill Perrin. While inTel'aran'rhiod Slayer attacks and kills Morninglight. Enraged, Perrin engages in combat with Slayer and is easily defeated. Before Slayer can finish him, Perrin manages to shift to another location. Slayer is then armed with a dreamspike and nullifies Perrin's use of moving his army with Traveling. After setting up the spike he continues to hunt and kill wolves who are trapped inside the dome. He attacks Perrin's pack shooting Sparks in the thigh and killing Whisperer. Hopper attacks Slayer while Perrin escapes with Sparks.
Perrin, with the aid of his wolf pack return toTel'aran'rhiod to confront Slayer. Perrin and Slayer begin to battle, with the wolves employing flanking tactics on him. Slayer manages to kill Oak Dancer and injure Sparks. Perrin's training in Tel'aran'rhiod begins to pay off with him nullifying all Slayer's attacks with willpower. Slayer becomes overwhelmed and retreats. During this time Perrin finds the dreamspike. Perrin takes the spike to Tar Valon, with Slayer close behind him, and the two begin struggling to take each other's life. After Slayer wounds Hopper, Perrin becomes enraged and knocks Slayer into a nightmare where Perrin stabs him in the stomach and destroys the dreamspike by throwing it into lava. Hopper tells Perrin he must go and seek answers from Boundless. Hopper then dies and Perrin leaves the Wolf Dream.
While recuperating in Town, Slayer (as Isam) is approached by a woman whom he believes to be an unrevealed Chosen but is Cyndane in disguise. She tasks him with killing Rand al'Thor as directly and efficiently as possible, and loans him the use of two Samma N'Sei and several guards to assist him, if necessary.
Slayer attempts to shoot Rand with an arrow while he is fighting Moridin in Shayol Ghul, but Perrin appears and deflects the arrow. Slayer shifts away to Samma N'Sei reinforcements. Perrin and Gaul follow and the men engage in battle. Slayer realizes that Perrin is in the flesh. They both charge at each other, but as Perrin is about to smash Slayer in the face with his hammer, Slayer shifts completely away, already prepared for this event. This begins another hunt with Slayer being the hunted and Perrin the hunter. Perrin has learned how to shift from the Wolf Dream to the waking world, like Slayer does, and in the end, Slayer is unable to defeat Perrin and he is killed by a blow to the head from Perrin's hammer, Mah'alleinir. Slayer was killed while in the form of Isam but it can be presumed that because of their link Luc died too.