An actor whose tall, rangy build and boyish good looks have made him a natural for comic roles, Diedrich Bader was born in Alexandria, VA, on Christmas Eve 1966; his father, William Bader, was Chief of Staff of the Senate Foreign Relations Committee during the Carter administration, and his mother, Gretta Bader, was a sculptor of note. When Bader was two, he and his family moved to Paris, France, where the boy was exposed to a steady diet of classic American comedies; young Bader was especially fond of Charlie Chaplin, and appeared on-stage for the first time at the age of four, imitating the Little Tramp at a revival theater during an unexpected intermission after a rare Chaplin film jammed in the projector. Bader and his family returned to the United States in time for him to enter high school, and he later attended the North Carolina School for the Arts. While vacationing in Santa Fe, NM, during spring break, Bader met a casting agent who lined up an audition for a small role in a television pilot. Bader ended up winning the leading role instead, and while the pilot never sold, it did prompt Bader to relocate to Los Angeles and begin pursuing an acting career full-time. He began landing guest spots on episodic television shows, including Cheers, The Fresh Prince of Bel Air, and Star Trek: The Next Generation. In 1993, Bader was cast as the Searcher on the television series Danger Theater, a short-lived spoof of action-adventure programs. Penelope Spheeris, who directed the Danger Theater episodes, remembered Bader when casting for her film The Beverly Hillbillies (1993), based on the popular sitcom of the '60s and '70s. Bader won the role of cheerful but slow-witted Jethro Bodine, and his performance was one of the comic highlights of the film. The movie significantly raised Bader's visibility, and in 1995 he was cast as the logically challenged Oswald on The Drew Carey Show. Bader's success on The Drew Carey Show led to notable supporting roles in motion pictures, such as Office Space and Jay and Silent Bob Strike Back; he also began doing voice work for a number of animated television projects, including Pepper Ann, Buzz Lightyear of Star Command, and Kim Possible. In his private life, Bader married actress Dulcy Rogers in 1998.
As his run on The Drew Carey Show continued, he also appeared regularly in feature film such as The Country Bears, Napoleon Dynamite, Eurotrip, and Miss Congeniality 2: Armed and Fabulous, as well as animated films like Ice Age and Bolt. In 2010 he landed a recurring role on the short-lived NBC sitcom Outsourced.