Movies
* The Magnificent Seven (1960) - As Britt, a member of the seven gunslingers. This is arguably his most iconic role.
* The Undefeated (1969) - Starring John Wayne, as "The Kid."
* The Good, the Bad and the Ugly (1966) - A small but memorable role as "The Soldier" in this Clint Eastwood classic.
* Support Your Local Sheriff! (1969) - A hilarious comedy starring James Garner, where Bertram plays "Jess."
* The Wild Bunch (1969) - Playing "Deke Thornton" in this iconic Sam Peckinpah western.
* The Last Man on Earth (1964) - A post-apocalyptic film starring Vincent Price, where Bertram plays "The Doctor."
* The Professionals (1966) - Starring Burt Lancaster and Lee Marvin, Bertram appears as "Dr. Mendoza."
* The Great Escape (1963) - Bertram plays the character of "P.O.W." in this war film classic.
* The War Wagon (1967) - A western starring John Wayne, Bertram plays "Milt."
Television
* The Wild Wild West (1966-1969) - As "The Chief" in the popular TV series.
* Bonanza (1961) - A guest appearance in this classic western.
* Gunsmoke (1955-1975) - Several guest appearances in this long-running western show.
* Have Gun – Will Travel (1957-1963) - Another guest appearance in this western series.
* The Virginian (1962-1971) - Another popular western series where Bertram appeared as a guest star.
Notable appearances in other television projects:
* Mission: Impossible (1966-1973)
* The Man from U.N.C.L.E. (1964-1968)
* The Twilight Zone (1959-1964)
William Bertram was a versatile actor who appeared in various roles, with a particular focus on Westerns. His film and television career spanned several decades, and he left a lasting impression on the world of entertainment.