After years on the circus and vaudeville circuits, Si Jenks came to films in 1931. Virtually always cast as a grizzled, toothless old codger, Jenks was a welcome presence in dozens of westerns. In Columbia's Tim McCoy series of the early 1930s, Jenks was often teamed with another specialist in old-coot roles, Walter Brennan (17 years younger than Jenks). In non-westerns, Si Jenks played town drunks, hillbillies and Oldest Living Citizens usually with names like Homer and Zeke until his retirement at the age of 76.