Marcus Korolus was born in Rome in the year 136. After becoming Immortal, he was mentored by Gaius Septimus. Marcus lived as an actor, and also mentored Walter Graham.
In the 1620s, Korolus was accused of witchcraft, and was burned alive. The fact that the woman he loved, Lenora, had betrayed him to such a fate, was too much for him, and Korolus went mad. In revenge, he murdered Lenora, taking her scalp. Her death alone didn't satisfy him, however, and he continued to kill other women in the same way. His targets were always women who reminded Korolus of Lenora, and had long blonde hair like she had.
In 1925, Korolus was an actor appearing in Seacouver's Orpheum Theater, starring in "Man and Superman". After ten women in that town were mysteriously murdered by someone dubbed "The Scalper", Duncan MacLeod started investigating the murders. He surprised Korolus by tracking him to the Orpheum when he was about to kill another woman. Duncan tried to persuade him to stop, but, finally realizing Korolus was insane, he had no choice but to challenge him. In the end, Duncan was victorious, and Korolus lost his head.
Korolus' legacy, however, would endure, and in 1992, a new killer, also dubbed "The Scalper," followed in Korolus' steps, killing women in the same places, or places related to the crime sites where Korolus had killed his victims. Recognizing the pattern, Duncan once again tried to stop the killer.
Walter Graham, Korolus' student, was a friend of Duncan's, although it is unknown if Graham knew Duncan had defeated his mentor, or even if he had a good relationship with Korolus.