He died of natural causes Thursday at the Motion Picture and Television Country House and Hospital, the Los Angeles Times reported Monday.
Cornthwaite was most proud of his role as the mad scientist in "The Thing," a 1951 horror movie about a group of scientists who find an alien frozen in the Arctic, the Times said. He also appeared in the 1953 "War of the Worlds" and his other film credits included the 1962 "What Ever Happened to Baby Jane?" in 1962. In the 1990s, he was a regular on TV's "Picket Fences."
Born on April 28, 1917 in St. Helens, Ore., Cornthwaite started acting in high school. He worked in radio in Southern California during college, continuing in radio after World War II.
That work led to television where he appeared on "Perry Mason," "The Twilight Zone," "The Monkees," "Studio 57," "Four Star Playhouse" and "Schlitz Playhouse of Stars."
Cornthwaite is survived by his brother and several nieces and nephews.