Robert Downey Jr.
Before 2003, Robert Downey Jr. was known more for his substance abuse problems and arrest record than he was for his acting career. Though he appeared in a handful of classic, successful films in '80s and early '90s (Less Than Zero, Air America, Chaplin, Natural Born Killers), between 1996 and 2001 his career had hit slump. He was written out of his role on Ally McBeal due to his issues, and his arrests even lost him a role in the successful Julia Roberts-starring romantic comedy America’s Sweethearts.
He went to rehab repeatedly and, after a few years of struggling with his recovery, finally ventured back into films in 2003 with a role in The Singing Detective (Downey Jr. was considered a high-risk hire at that time, and only got the gig after his friend and Air America co-star Mel Gibson paid for his insurance). What followed was a string of successful films, including Good Night, and Good Luck, and A Scanner Darkly, but it wasn’t until he was cast as Tony Stark in 2008’s Iron Man that his career really took off again. He’s now clean and considered one of Hollywood’s most high profile and respected actors. Take note, Lindsay Lohan.