Morgan Walker was a sailor, until he died in 1671 in a storm off the coast of Gibraltar.
In 1808, Walker commanded the slave ship Meurtrier. He owned a house in New Orleans, and earned his living by trading slaves. When he came back a few days early from a trip, he sensed an Immortal near his house. His favorite slave, Charlotte Johnson, whom he kept as a concubine, denied that anyone had been with her. Walker believed she was lying and threw her out the window in anger and killed her.
On the street, Walker accosted an Immortal, whom he knew as Dr. Benjamin Adams. He accused Dr. Adams of cuckolding him with Charlotte and challenged him, but the Doctor refused to fight. Walker pursued him as far north as Charleston, where Dr. Adams boarded a ship and left him behind. Walker never got over the man who would not fight him and held the grudge for almost 200 years.
In the late 20th century, Walker lived in Paris and owned a modeling agency, as well as a secret sex trafficking operation. By chance, he bumped into Dr. Adams for the first time in two centuries. Benjamin Adams had been merely one of the many aliases Methos had utilized over the years, and he again refused to fight Walker and walked away.
The rookie Watcher, Amy Thomas, had been recently assigned to Walker, whom she learned to despise. Amy was indiscreet enough to be spotted and captured by Walker.
With Amy's disappearance, Joe Dawson turns to Methos for help. Joe and Methos both repair the hurt engendered by Methos abandoning Joe to bury Richie alone at the time of Richie Ryan's death, and begin to develop a new appreciation for one another during the pursuit of Walker. Once cornered in an abandoned building by Walker's thugs, Joe admitted that Amy was his daughter. While Methos took out the goons, Walker called Joe on his cell and offers a trade: Amy for "Dr. Adams" and Joe agreed, though he was wracked with guilt by it, making it obvious to the canny Methos what has happened
Methos ran a guilt trip on Joe until finally Joe broke and revealed the trap. Methos nods, "That wasn't so hard was it?" he asks. When Joe reacts angrily, Methos points out the holes in Joe's story and the fact that Joe was a terrible liar. When Joe demands to know why Methos dragged it out, Methos cheerfully admits, "I'm easily amused."Joe and Methos meet Walker together, with Joe promising that if Walker hurts Amy, "I will shoot you. And I will make sure the doctor takes your head." Methos takes the long postponed challenge from Walker as Joe and Amy move to safety. "Take a walk, Joe. Take Amy with you. This is between me and him." To which Walker replies "That's all I've ever wanted."
Methos proved once again, "Just because I don't like to fight, doesn't mean that I can't."