-- For decades, Robin Williams seemed nothing but jovial in many of his award-winning films, TV appearances and stand-up routines.
However, privately, the actor, who died of a suspected suicide Monday, struggled with demons.
"He has been battling severe depression of late," his publicist told ABC News. "This is a tragic and sudden loss. The family respectfully asks for their privacy as they grieve during this very difficult time."
Williams, who was 63 at the time of his death, had also struggled with substance abuse in the late '70's and early '80's. However, after his friend John Belushi died of an overdose in 1982, and his son, Zachary, was born in 1983, Williams quit cold turkey.
"The one thing that cleaned me up from that was having a kid," he told Nightline in 2011. "That's immediate. I didn't have any rehabs or groups. I just kind of took my mother's advice of vitamins and exercise. You realize, OK, now you have this responsibility, and [I] dealt with it."
In 2006, he began drinking again. This prompted him to check into a rehab facility.
"It's [addiction] -- not caused by anything, it's just there," Williams said. "It waits. It lays in wait for the time when you think, 'It's fine now, I'm OK.' Then, the next thing you know, it's not OK. Then you realize, 'Where am I? I didn't realize I was in Cleveland.'"
His commitment to maintain his sobriety was such that this past July, Williams scheduled another visit to a treatment facility. A source told ABC News at the time that he had not relapsed.
"After working back-to-back projects, Robin is simply taking the opportunity to fine-tune and focus on his continued commitment, of which he remains extremely proud," a rep for the actor told ABC News at the time.