Allen Francis Doyle's History
Angel Investigations
Doyle was born in Ireland to a human mother and a Brachen demon father. Doyle never knew his father or anyone on that side of his family, and his own demonic genes didn't physically manifest themselves until he was 21 years old.
At the time, Doyle was a third grade teacher and soup kitchen volunteer, married to a woman named Harriet and considering having kids of their own. He didn't take the news of his demonic heritage well, in spite of Harriet's acceptance of his other side, so his marriage ultimately disintegrated.
Four years later, he was approached by a fellow Brachen demon, Lucas, who told Doyle that the Scourge, a militant group of pure blood demons, was after all half-breeds and begged for Doyle's help. Doyle turned Lucas away, believing that this wasn't his problem. Soon after, he received a vision, which he described as "splittin' migraines that come with pictures," in the throes of which he thought he was having a stroke. The vision showed him a group of massacred Brachen demons. Doyle searched the city to find out if what he had seen was real — it was.
These visions, which came from the Powers That Be, were what led Doyle to the ensouled vampire Angel. As Doyle said "We all got something to atone for," so the two joined forces to fight evil in Los Angeles. Once Cordelia Chase joined the team, Angel Investigations was officially formed. Some point around that time, he came to own an apartment.
Doyle soon fell for Cordelia, but was afraid she would reject him upon finding out about his demonic heritage, a belief reinforced by Cordelia's open black-and-white view of demons being evil. He also forms a close, brotherly bond with Angel. Despite Doyle's reluctance to discuss his past, Angel and Cordelia learned more about him when Harriet returned to his life, seeking a divorce so she could marry an Ano-Movic demon named Richard Straley. Harriet later called the marriage off after learning that obtaining the blessing of the Straley clan would require Richard to kill the ex-husband of his intended bride by eating his brain.
Sacrifice
Doyle's past again came back to haunt him when the Scourge returned, threatening the Lister Clan, another tribe of demons regarded as half-breeds. To save their lives as well as those of Angel and Cordelia, Doyle sacrificed his own life to disable the Beacon, a device which could destroy any being "tainted" with human DNA, leaping on to the Beacon and pulling out a vital power cable, being disintegrated by its energy output just as he deactivated it.
In doing so, Doyle fulfilled the Listers' prophecy of the Promised One, a being purported to save them from the Scourge in the last days of the 20th century. Before Doyle died, he shared a kiss with Cordelia, who had only recently learned of — and accepted — Doyle's demonic heritage, and lamented that they would never know if she could come to fully love him as a half-demon. With this kiss, his visions passed on to her.
Legacy
After Doyle's death, Angel confronted The Oracles, asking them to rewind time to give him a chance to resurrect Doyle, but they refused, as doing so would render Doyle's very act of sacrifice and redemption meaningless.
In an alternate reality, Cordelia never joined Angel Investigations and Doyle passed his visions to this alternate Angel before dying. This eventually resulted in Angel having a mental breakdown, unable to handle the strain of the visions, especially in absence of Cordelia's humanizing influence, with only the alternate Wesley — here lacking one arm — and alternate Gunn for company.
When Lindsey McDonald returned to Los Angeles in 2003, he assumed Doyle's identity in an ultimately failed attempt to convince Angel and Spike that the latter was the subject of the Shanshu Prophecy. Both Angel and Cordelia were outraged and disgusted that Lindsey stooped so low as to abuse Doyle's name and legacy.
