who played mark in the original roseanne series
Glenn Quinn Glenn Martin Christopher Francis Quinn (May 28, 1970 â€“ December 3, 2002) was an Irish actor. While he was best known for his portrayal of Mark Healy on the popular '90s family sitcom Roseanne, Quinn also amassed a large fan base for his portrayal of Doyle, a half-demon, on Angel, a spin-off series of Buffy the Vampire Slayer.[1][2]
Johnny Galecki John Mark Galecki (born April 30, 1975)[1] is an American actor. He is known for playing David Healy in the ABC sitcom Roseanne from 1992â€“1997 and Dr. Leonard Hofstadter in the CBS sitcom The Big Bang Theory since 2007. Galecki also appeared in the films National Lampoon's Christmas Vacation (1989), Prancer (1989), Suicide Kings (1997), I Know What You Did Last Summer (1997), Bookies (2003), and In Time (2011).