Rack's History
Sunnydale
Rack was a dark warlock who had, apparently, resided in Sunnydale at least since 1998, when Amy last visited him before becoming a rat. He was the mystical equivalent of a drug dealer, but he would share his magic only after the recipient allowed him to explore his or her mentality.
He was apparently well known within the demon community, as demons were scared of his very name and refused to help guide anyone to him. Spike recognized his name and was alarmed to learn that Willow was in his company, while Clem initially resisted to lead Dawn to Rack's residence and refused to enter it.
Rack's hideout was cloaked so that only demons and those with magic abilities could find it. Once inside, there was a waiting room with several people, and a back room where he lived and did magic.
In 2001, Amy took Willow to visit Rack after they had exhausted all their own magics at the Bronze on the previous night. The price for Willow's first taste of magic from Rack was his insistence on "having a taste" of her. After this, Willow and Amy spent several hours with Rack. Willow's addiction to magic became more pronounced and she went back to Rack's apartment the next night with Dawn in tow. Leaving Dawn alone in the waiting room, Willow stayed in Rack's room time enough for them to miss an entire movie, being high on magic, again on the ceiling.
Upon leaving Rack's place, they were attacked by Mandraz, a demon who claimed that Willow summoned him, the price to pay for using such potent magics. In order to escape, Willow stole and magically drove a car, showing her hands-off driving ability to Dawn, laughing and swerving playfully without watching the road. This led to an accident in which Dawn's arm was broken, then Willow confessed to Buffy that she was addicted and needed help. Willow renounced her magic and severed her contact with Rack and Amy.
After Warren Mears discovered Buffy had survived his assassination attempt, he paid Rack for protection from the Slayer. Rack warned Warren that Buffy was the least of his problems compared to "the witch" (Willow). Rack gave Warren protection enough for Willow to mistake his robot for the real Warren, and sent him on his way, though he warned Warren that there was no guarantee that they would stop Willow. Shortly thereafter, Willow, corrupted with dark magic, visited Rack and drained his magic into her, leaving him unconscious and hanging upside down from the ceiling. Since then, she believed to had killed the warlock.
Marrack
Rack lost his powers and was in a coma for a month. At some point, though, he regained his magic and found himself as a traveler in alternative dimensions. During the end of magic, Rack became trapped in a mystical dimension, where he would encounter Willow on a mission to restore magic to their home dimension. Rack disguised himself in a demonic form, introduced himself to her as Marrak, and became her traveling companion, having earned her trust by rescuing her from attacking wing-heads: demons which contain dreams and nightmares from Earth.
While traveling, Willow was reunited with her long-lost lover, Aluwyn, and her "super coven" of traveling witches. Marrak tried to dissuade Willow from losing sight of her mission, but he was banished from the witches' paradise for his impertinence. Later, he appeared to Willow in her dreams using the wing-heads to inform her that her magical paradise was an illusion and that she was being kept on a perpetual "high" while the Earth suffered.
Remembering her friends, Willow parted ways with Aluwyn and returned to Marrak's company, only to find him more covetous of dark magic, having absorbed all the dark magic of the wing-heads. It was then Willow realized who he truly was, and she attacked him with a magical blast which restored his true form.
Revealed, Rack vowed to steal Willow's magic away from her much as she had stolen his. In their magical duel, they saw themselves inside a mystical embodiment of the universe, where its antibodies attacked and "removed" Rack for causing it harm. Willow survived for having learned to become a balanced being
