Dick Beals, who also voiced the lead character in TV's Davey & Goliath, was 85.
Beals suffered from a glandular condition which left him with the body and voice of a child.
His distinctive childlike qualities helped the actor become a hit in broadcasting in the 1940s, when he was first heard on radio shows like The Lone Ranger and The Green Hornet.
He moved to Hollywood in 1952 and signed on to front Alka-Seltzer ads as animated sprite Speedy.
The character was featured in more than 200 commercials that aired from 1954 to 1964, according to the Los Angeles Times.
As well as his roles in Davey & Goliath and The Gumby Show, Beals also sang with Gene Kelly in the 1967 TV special Jack and the Beanstalk and he beat out 300 child actors for the role of N.J. Normanmeyer in the early 1990s animated series The Addams Family - at the age of 65.
Away from Hollywood, Beals opened an ad agency in his adopted Escondido, California and served as a high school sports announcer.