Doyle was introduced in the first episode of Angel's first season, as Angel's guide to The
Powers That Be.  Doyle was half demon and half human, and had what might be
considered a gift, of future visions.  He had developed quite the little crush on Cordelia,
and in fact hid his demon-half from her, thinking she would hate him for it.  In the
mean time, she didn't realize how important he had become to her until he died in
order  to save her, Angel and a group of ragtag demons.  He kissed her goodbye, gave
her his gift, and then sacrificed himself.
Glenn Quinn is Doyle
Glenn Quinn was born, and raised, in Ireland on May 28th, 1970. He moved to the United States at the age of 19, and, prior to his role as
Doyle, was best known to American audiences as Becky Conner's not-too-bright husband Mark on the long running sitcom
Roseanne.  
Quinn tried to get back to Ireland as often as possible. Although he spent years "doing" an American accent on
Roseanne, he was pleased
that producers made Doyle Irish when he was cast. In an interview with The Irish Times, Quinn said of his accent "I've been hiding it for
so long that it's amazing to have some freedom. It was like putting on an old pair of shoe
's ”it's bringing my soul back to life."  In addition to
acting, Quinn played the drums and guitar, and was part owner of Goldfingers, a Los Angeles nightclub with a 007 motif.  Sadly, Glenn
Quinn died of an apparent drug overdose, in December 2002.  
Story here.