Test Text1 plain A brilliant light has gone out in Hollywood tonight. Robin Williams, whose fierce, frenetic comedy captivated us for decades has died at age 63. For all his wild, often improviced... See More
Test Text1 plain A brilliant light has gone out in Hollywood tonight. Robin Williams, whose fierce, frenetic comedy captivated us for decades has died at age 63. For all his wild, often improviced humor on stage and on screen, behind the scenes he struggled mightily with substance abuse and depression. Tonight on a special edition of "Nightline" we're going to dedicate our entire show to the life and the death of a true American original. Nano-nano. Reporter: From Mork -- Shazbat. Reporter: To captain hook. To Mrs. Doubtfire. To his manic make you laugh so hard your ribs hurt comedy specials. Oh, yeah! Reporter: Robin Williams was a legend. But behind the zaniness lurked something darker. Drug abuse and depression. Williams described himself as a man looking over a cliff. It's not just a fear of falling or -- it's the thing of, you can do this. You can jump. You know. You can fly. And just one. For someone who has no tolerance for it, that's not a possibility. Reporter: And this morning, according to authorities in California, they got a 911 call reporting that Williams was not breathing at his home in tiburon. They're calling it a case of suspected suicide. Tonight his representatives saying Williams had been battling severe depression of late. ABC news has learned Williams recently checked himself back into rehab. His wife Susan Schneider issuing a statement tonight saying, "I lost my husband and my best friend. I am utterly heartbroken." A tidal wave of sadness and sympathy online tonight from fans and fellow celebrities. Steve martin tweeting, "I could not be more stunned by the loss of robin Williams. Great merge, acting partner, genuine soul." John travolta, "We loved him and he loved us back. We are all better for having known him. I love you, robin." And so many more tonight. Bill Cosby, Tim Allen, Kevin spacey, Reba Mcintyre, and this from Ellen degeneris. "I can't believe the news about robin Williams. He gave so much to so many people. I'm heartbroken." We spoke by phone tonight with Cheryl hinds who guest starred on Williams' recent CBS sitcom "The crazy ones." It's so hard right now because it's so tragic. But I just feel very thankful and grateful that I got to work with him and I got to -- to be his friend. Reporter: Even president Obama weighing in tonight. "He was one of a find kind. He arrived in our lives as an alyen but he ended up touching every element of the human spirit." And in Hollywood itself tonight at the iconic comedy club the laugh factory, where Williams performed many times, a tribute right there on the marquee. "Robin Williams, rest in peace, make god laugh." For Williams, life began in Chicago in 1951. His mother, a former model. His father, an executive at Ford. He was surprisingly a quiet child. The first comic impression he did imitating his grandmother to his mom. It was only in high school, in drama class, that he overcame that shyness. He went on to julliard and shortly thereafter, in the late 1970s, he burst into the national consciousness as an oddball alien named Mork. Nano-nano. Reporter: In the TV show "Mork and Mindy." He ad libbed most of his dialogue and his wild physical comedy. The show was a huge hit. Then came a series of live comedy specials, also big hits. We believe now that chernobyl has been taken care of. If you'd like to follow us into the plant I'll show you around. Reporter: And then of course the movies. ? Reporter: There was that unforgettable role in "Popeye." Williams very quickly moved into dramatic territory. With "The world according to gap" in 1982 about a struggling writer and his romantic entanglements. I wrote a short story. I wrote it for you. You wrote it for me. Many of his most famous roles mixed wit and warmth. "Good morning Vietnam." What is the demilitarized zone? Sounds like something from "The with zard of oz." Reporter: "The dead poet society." Call me Mr. Keating or if you're daring captain my captain. Reporter: "Mrs. Doubtfire." And "Good will hunting." Talk about you, who you are. And I'm fascinated. I'm in. Reporter: For which he won an Oscar for best supporting actor. All that onscreen humor masked inner turmoil. If the early 1980s, a problem with cocaine which he claimed to have quit after the fatal overdose of his friend and fellow comedian josh belushi. He spoke to ABC's Barbara Walters about it. People also feel in writing about you, Reading the interviews, that the December of josh belushi was an enormous influence on you, rather than just -- you tell me what it was for you. It's only the fact that, here's a guy who is probably one of the toughest, strongest people you could ever meet. And he's taken out. You know? It's -- basically it cleaned up a whole generation of people. Because this guy was as strong as anybody you could ever meet. John could run into that wall and get up and do it again. If it took him out, yous. Th -- you realize we're all pretty motel. You hear about people using drugs, they use it to get high. For me it was a great way of escaping, to cut off from people. It was the only time I could escape. Reporter: He got sober for many years, it appears. But then he relapsed as he discussed on his comedy tour "Weapons of self-destruction." Alcohol is dangerous for peel like myself, alcoholics. Or ethanol challenged, whatever you want to call it. Reporter: Williams checked himself into rehab in 2006. He talked about it in this interview with ABC's Diane sawyer. So to talk about it as caused by something -- It's not caused by anything, it's just there. Latent. Waits. It lays in wait for the time when you think, I'm fine now. I'm okay. And then, beep. And then next thing you know, it's not okay. You realize, where am I? This is strange, I didn't realize I was in Cleveland. How are you? I am well. Very well. It is a good thing. Is it a good thing? Oh, yeah, it's nice. Two months? Two months. Club medicated. Oh, wait. Quiet time. I'm back. People say, how do you feel? With my fingers. How is that? Don't drink. What are you doing to stay that way? Don't drink. Reporter: Relapse caused him his second marriage. He sought to clean up his act for the sake of his career and most importantly his three children as discussed in this interview. The one thing that cleaned me up, that was having a kid. That's immediate. I didn't have any rehab or any group -- You did it yourself. Oh, totally. Kind of -- I took my mother's advice. Vitamins and exercise. When you have a kid you're awake and smell like piss anyway so you don't need drugs. You're like, hey, where's the baby? Reporter: It is fitting his final posting on social media was a tribute to the daughter he loved. "Happy birthday to Ms. Zelda ray. Rae Williams, quarter of a sench wrench old today but always my baby girl. Happy birth de, Zelda Williams, love you." If the 60-year-old robin Williams could give the 30-year-old robin Williams advice, what would you tell him? Don't go so fast. How much have you loved doing what you do, loved being with people? If you can answer that question positively, you're doing okay. It's a good life. And just before we came on the air tonight, one of the people Williams loved very much, his daughter Zelda Williams, said on Twitter, "I love you, I miss you, I'll keep trying to look up." So much pain for his family tonight. We're thinking about them.
This transcript has been automatically generated and may not be 100% accurate.