Alfed Cahill was a mentally unstable Englishman who had served in the British Royal Air Force in the early 1970s, but had been discharged for failing a psychological exam. His mental breakdown was partially the end result of years of abuse from his father.
In 1993, Cahill was in Paris, talking to a prostitute named Claudine. When she doubted what he said, he became angry and hit her. A general fight broke out, and he beat his way through the crowd to her. When he said he was going to correct her 'nasty attitude' and raised a fist, she stabbed him.Cahill staggered away from the club and through the streets of Paris, finally dying in front of a Crusader museum. Cahill awoke pulled the knife from his chest and proclaimed it a miracle. But Cahill did not die alone, as Duncan MacLeod had spotted him when he was running through the streets and had seen him die. Despite MacLeod's attempt to explain to him about Immortality and The Game, Cahill already believed that he had reborn as an avenging angel set out by God to rid the world of sin and left MacLeod.
Cahill then began a killing spree, murdering Claudine, her pimp's driver, and a prostitute's client. Duncan began to investigate the murders and realized the next victim would be Elaine Trent, a call girl who had been Tessa Noël's college friend, since the man murdered was her client.
MacLeod tried to persuade her to leave Paris, but her pimp, Dominique Battini, interfered. They had an argument which resulted in Battini lying on the floor while Duncan took Elaine to his barge. In an attempt to kill Elaine at her apartment, Cahill ended up meeting and killing Battini. MacLeod confronted him, but Cahill sought refuge in the museum where he had died. There he waited for MacLeod who soon found him - dressed as a Crusader.Unwilling to accept MacLeod's help, Cahill foolishly believed he could not be killed, not knowing the rules and limitations of his immortality, and challenged MacLeod. He soon lost his head.
Obsessive and manic, his transition to immortality caused a psychotic break in an all ready borderline personality.
Although trained in martial arts as an SAS commando, he had no training at all as a swordsman, and never got the chance.