Let me fill in a bit of biographical background to flesh out who Gary Oldman is when he isn't acting, which is covered quite well above.
He was born Gary Leonard Oldman in south-east London in 1958 in a solidly working class family. His father was a welder and an alcoholic who left the family when Gary was only seven; his mother raised the boy and his two sisters alone after that. Gary never got to know his father well. If you want to get a feel for Gary's childhood, watch the movie Nil By Mouth, which he wrote and directed; the similarities between his life and that portrayed in the movie suggest that it was based on his own experiences.
Gary dropped out of school at sixteen and worked at a sports equipment store; around this time he seems to have discovered his keen intelligence. He started to read and taught himself piano; he is an accomplished pianist and actually played many of the passages in Immortal Beloved. He initially considered a career in music, but soon became interested in acting, and won a scholarship to the Rose Bruford Drama College, from where he received a B.A. in Theatre Arts in 1979. Thereafter he worked in the theatre for a number of years, appearing in plays with the Royal Court Theatre and the Royal Shakespeare Company. He won a number of awards for his performances.
In the late 1980s he married Lesley Manville; the two have a son, Alfie, but the marriage only lasted two years. In 1990 he married actor Uma Thurman; this union dissolved after two years. During filming of Immortal Beloved he became involved with co-star Isabella Rosselini, but the two soon broke up.
Part of what made his private life so turbulent was his alcoholism; eventually he took the path of many creative types and went into rehab; there he met American photographer Donya Fiorentino; the two married in 1997 and now have two sons.
In spite of the dark roles he plays, he is said to be a charming and fun guy, and a consummate professional, particularly since he has kicked his drinking habit. A great actor.