Doyle is a human/demon hybrid who recieves visions from the Powers That Be. Doyle is more known for wanting to find a drink instead of helping people until the Powers tell him of Angel. 
   

  Doyle finds Angel and gives him a warning of a woman mixed up with a vampire assocated with Wolfram&Hart. Doyle later helps Angel when Angel learns that the vampires next victim will be Cordelia Chase . Cordelia realizes that the man is a vampire and runs out of the room where she finds Angel. After saving Cordelia;and Doyle helping Angel with his visions Angel investigations is created.  
 
   Doyle helps Angel with multiple cases while crushing on Cordelia. His next big problem is when an Avok Demon comes to collect Doyle's debts. He has Angel help him by standing up to the demon. Angel convinces him to let Doyle pay insted of taking his life. The demon still comes after Doyle but the demon and his men are killed by a ghost living in Cordelia's apartment. 
 
   Part of Doyle's past is reveiled when Doyle's wife Harry, comes back telling how she has plans to marry an Ano-Movic demon named Richard. She brings divorce papers, depressing Doyle. When Richard invites Doyle and Angel,  Doyle agrees trying to heal the wounds. Richard and his family later return to old Ano-Movic ways and try to eat Doyle's brains to insure a happy mariagge. Angel breaks it up and Harry comes in telling Richard it's over because she does not approve of the canabalistic demon ways. 
 
  In Doyle's final episode The Scourge come back from his past to kill a family of human/demon hybrids. It shows a flash back of another human/demon hybrid asking Doyle for his help or else that the Scourge will kill his family. Doyle and the human/demon familly along with Cordelia and Angel are locked in a cargo boats under carrier,along with a machine that kills anyone with human blood in them. Angel attempts to save them but Doyle knocks him out. Doyle shares a passionate kiss with Cordelia passing on his visions to her. He unplugs the cable to the device and burns up right after. 
 

Powers 

Doyle has visions from the Powers That Be showing him people in trouble. Doyle often describes the visions as "Splitting Headaches with Pictures". 
Cordelia later describes the visions as being twice as painful as they look and that they are "scratch and sniff visions".
 
Outside of his Visions, as a demonic Halfbreed, Doyle posesses several other powers whilst in his demon form. It is shown that his sense of smell is greatly increased as he is able to track Angel's movements inside of a rat-infested sewer in order to find the Ring of Amara. He is able find the Ring virtually instantaneously after only having been in his Demon form for seconds. 
It is also stated that Doyle is far stronger in his Demonic form, though he nevertheless usually chooses to fight in his human state, so as to avoid revealing his roots.