Williams had been battling severe depression, according to his publicist.
Neighbors said he appeared to lead a normal, ordinary life at home, a contrast to the extraordinary world he created as an actor and comedian.
The Juilliard trained actor also excelled in dramatic roles, like "Good Will Hunting" which brought him a Best Supporting Actor Oscar.
Williams' wife released a statement saying, "It is our hope the focus will not be on Robin's death, but on the countless moments of joy and laughter he gave to millions."
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