He became known for his role as Leonard Hofstadter on the CBS sitcom The Big Bang Theory and as David Healy on hit sitcom, Roseanne.
He appeared as Rusty Griswold in the 1989 film, National Lampoon's Christmas Vacation, and in 2011, he made a guest appearance on Entourage as himself.
He dated his Big Bang Theory co-star and love interest, Kaley Cuoco, for two years while on the show.
He was raised by a marriage councilor mother and a rehabilitation instructor father and made his acting debut in the 1987 mini-series, Murder Ordained at age 12.
He began dating actress
Kelli Garnerin 2011.