SAN RAFAEL, Calif. (AP) — Oscar-winner Robin Williams, whose free-form comedy and adept impressions dazzled audiences for decades, has died in an apparent suicide. He was 63.

The Marin County Sheriff's Office says Williams was pronounced dead at his home in California on Monday. The sheriff's office says a preliminary investigation shows the cause of death to be a suicide due to asphyxia.

Williams shot to fame in the late '70s as the alien in TV's “Mork and Mindy.” He conquered the big screen in comic films such as “Good Morning, Vietnam” and “Mrs. Doubtfire.” But he won his Academy Award in a serious role — as the therapist in “Good Will Hunting.”

His performing style was at its purest in his standup act, as he impersonated a Russian immigrant or parodied anyone from John Wayne to Keith Richards.