Glenn Martin Christopher Francis Quinn (May 28, 1970 – December 3, 2002) was an Irish actor in television and film, known for playing Mark Healy in the American sitcom "Roseanne", and Doyle, a half-demon, on "Angel", a spin-off series of "Buffy the Vampire Slayer".
Glenn Martin Christopher Francis Quinn was in his 40s when he died.
He died in his 30s. It may have been difficult because it involves doing math. 