- Ralph Malph on The Fonz and the Happy Days Gang
- The lute instructor in Hägar the Horrible: Hägar Knows Best
Most was a student at Lehigh University in Bethlehem, Pennsylvania. He and Anson Williams were to be the stars of a proposed Happy Days spin-off centering on their characters of Ralph and Potsie, but those plans were never fulfilled. In February 2009, Most appeared with Henry Winkler for a Happy Days reunion at the World of Wheels in Birmingham, Alabama.
Most has two daughters with actress Morgan Hart, to whom he has been married since 1982.
- Donny Most at the Internet Movie Database