He was portrayed by the late Rance Howard, David Boreanaz, and Paul Logan.
Marcus Roscoe was a retired salesman who was adept at forcibly exchanging bodies with young athletic men to engage in adventures, having acquired a mystical urn and enchantment that allowed him to switch souls with others. Despite the fact that the transference was only temporary, with the younger bodies inevitably collapsing into a pile of skin after a certain amount of time, he nevertheless continued, his 'selected' victims being the members of the health club opposite his retirement home. His scheme came to a head when he switched bodies with Angel after the vampire came to question him for information about the deaths of the club members. Initially, he managed to escape detection despite his minor misconceptions- he assumed that he and Cordelia were going to the Hyperion Hotel for a romantic liason rather than because it was a place of work and initially thought that Angel was gay after being told he needed to talk with Fred before learning that 'Fred' was a woman (After initially assuming that it was Wesley)-, but after he instinctively 'vamped out' while making out with Lilah Morgan- who had recently made Angel's acquisition of the hotel legal as part of her plan to upstage her firm rival Gavin Park-, he realised his true vampire nature. Angel's friends initially assumed that Angel had reverted back to Angelus, but this notion was quickly dispelled when they discovered that Marcus had been reading books about vampires, something that neither Angel or Angelus would need to do.
Having spent a few hours at a club, Marcus returned to the retirement home to confront Angel, having finally discovered the 'perfect' body- one that would never collapse-, taunting Angel about how he was a pathetic example of a vampire due to them killing people rather than helping them. Before he could kill Angel, however, he was attacked and knocked out by Angel's friends, Angel subsequently reversing the spell after they dragged Marcus back to his room. Afterwards, Angel destroys the orb he used to perform the body swaps, preventing him from doing it again. As the team departed, Marcus yelled after Angel that he didn't deserve that body, only to suffer a heart attack as Angel coldly informed Marcus that the reason he had a weak heart was that he didn't use it much.
What became of Marcus after the team's departure is unknown, but given that his body had already suffered a previous heart attack while Angel was in it, it seems likely that he is now deceased.