William David Daniels (born March 31, 1927) is an American actor, who is best known for his television roles, notably as Mark Craig in the drama series St. Elsewhere, for which he won two Primetime Emmy Awards; the voice of KITT in the television series Knight Rider; and as George Feeny in the sitcom Boy Meets World, which earned him four People's Choice Award nominations. He reprised his Knight Rider role in the sequel TV movie Knight Rider 2000 and his Boy Meets World role in the sequel series Girl Meets World. He also portrayed Carter Nash (actual identity of the eponymous comedic superhero) in Captain Nice.

Daniels' film roles include Mr. Braddock (Benjamin Braddock's father) in The Graduate, Howard Maxwell-Manchester in Two for the Road, and John Adams in the musical film 1776. He was president of the Screen Actors Guild from 1999 to 2001 and led the union's efforts during the 2000 commercial actors strike.

Daniels is also noted for having portrayed in film or on television the three most prominent members of the Adams political family: John Adams, his cousin and fellow founding father, Samuel Adams, and John Adams’ son John Quincy Adams.