Jeff was born in Los Angeles, California, as the eldest child to a family that later relocated to San Jose when he was just a baby. He spent his formative years in San Jose, graduating from both grammar school and high school, as well as San Jose State Teachers College.
In college, Jeff pursued a degree in writing, simultaneously honing his skills as an amateur boxer and even becoming the runner-up in the Pacific Coast Golden Gloves competition. However, after realizing he lacked talent for writing, he decided to turn his attention to professional boxing, fighting for a year and a half.
Jeff's boxing career eventually led him to bluff his way into a stock company, which in turn, landed him a role in the Federal Theater Project. This experience ultimately led to his starring roles in Terry and the Pirates (1940) and Li'l Abner (1940).
However, his promising start was abruptly halted when the army called him in 1941. Jeff was discharged in October of the same year, only to find that there were no film roles awaiting him. It wasn't until he met Garson Kanin in the army that he was directed to a screen test in New York, which caught the attention of Louis B. Mayer of MGM, ultimately leading to a contract offer.
After signing his contract, Jeff was recalled by the army in February 1942 and remained there until his discharge in March 1945. Upon his return to MGM, he received roles in They Were Expendable (1945) and The Postman Always Rings Twice (1946). Unfortunately, his option was dropped shortly after.
Jeff, however, didn't let this setback deter him, and he instead turned his attention to television. His role as John L. Sullivan on a national television show led to his iconic role as Mike Fink, the legendary American keel-boat king. Walt Disney had two prerequisites for the role: a big, bluff build and a personality to match.
On the strength of his performance as Mike Fink, Jeff was signed for Disneyland TV productions, where he went on to star alongside Fess Parker and Buddy Ebsen in the fictional adventures of Davy Crockett. Jeff was known for his regular exercise routine, which included dining on steaks and salads, and his resonant singing voice, which he showcased in the Davy Crockett show by singing "The Mike Fink Boatman's Song."
