The Kroffts reacted on Twitter to the news of her death:
More recently, Hayes served as a voice actor for The Black Cauldron (1985) and for such cartoons as Trollkins, The New Scooby-Doo Mysteries, Paw Paws, Darkwing Duck, The Brothers Flub and Transformers: Rescue Bots.
Born on Aug. 5, 1924, in DuQuoin, Illinois, Hayes played in bandleader Vince Genovese's orchestra while in high school, then toured with her own singing and dancing act throughout the Midwest.
After moving to New York, she auditioned for theater legend J.J. Shubert and was hired for principle roles in three roadshow operettas: Student Prince, The Merry Widow and Blossom Time.
Hayes made her Broadway debut in Leonard Sillman's New Faces of 1956, then succeeded Charlotte Rae as Mammy Yokum in Li'l Abner. She played the bare-knuckle champion of Dogpatch for the remainder of its Broadway run through July 1958, then segued to the 1959 Paramount big-screen version that also starred Peter Palmer, Leslie Parrish, Stubby Kaye, Julie Newmar and Stella Stevens. (Hayes portrayed Mammy Yokum again in a 1971 ABC telefilm.)
In 1966, she toured with the national company of Hello, Dolly!, starring Betty Grable, and later appeared on such TV shows as The Monkees, Bewitched, Trapper John, M.D. and General Hospital.
Survivors include her niece, Nancy, and nephews Tom, Louie and Guy.
Donations in her memory can be made to the humane organization she founded: Pet Hope, P.O. Box 69493, West Hollywood CA 90048.
This article originally appeared in THR.com.