1. Patrick Stewart
No list of great American Dad! guest stars would be complete without Patrick Stewart, who lends the voice to Stan's CIA boss Avery Bullock in various episodes. Stewart is the most prolific guest star on the show, appearing in almost 60 episodes, and mentors Stand and his fellow agents, though is shown to be unorthodox in his methods and immature at times. Bullock cheats on his wife at various stages, and even sleeps with Stan's daughter Hayley, while he is shown to enjoy fishing, table tennis and hand to hand combat, serving as Stan's bane at times. Stewart is best known for his roles as Captain Jean-Luc Picard in Star Trek: The Next Generation and Professor Charles Xavier in the X-Men films.
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