Also I'd never even heard of David Carradine before this topic
Also a quick Wiki peek:
Bruce Lee's involvement In her memoirs, Bruce Lee's widow, Linda Lee Cadwell, asserts that Lee created the concept for the series, which was then stolen by Warner Bros.[8] There is circumstantial evidence for this in a December 8, 1971 television interview that Bruce Lee gave on The Pierre Berton Show. In the interview, Lee stated that he had developed a concept for a television series called The Warrior, meant to star himself, about a martial artist in the American Old West (the same concept as Kung Fu, which aired the following year), but that he was having trouble pitching it to Warner Brothers and Paramount.
In the interview, Pierre Berton commented, "There's a pretty good chance that you'll get a TV series in the States called 'The Warrior', in it, where you use what, the Martial Arts in Western setting?"
Lee responded, "That was the original idea, ...both of them [Warner and Paramount], I think, they want me to be in a modernized type of a thing, and they think that the Western type of thing is out. Whereas I want to do the Western. Because, you see, how else can you justify all of the punching and kicking and violence, except in the period of the West?"
Later in the interview, Berton asked Lee about "the problems that you face as a Chinese hero in an American series. Have people come up in the industry and said 'well, we don't know how the audience are going to take a non-American'?"
Lee replied, "Well, such question has been raised, in fact, it is being discussed. That is why The Warrior is probably not going to be on." Lee adds, "They think that business-wise it is a risk. I don't blame them. If the situation were reversed, and an American star were to come to Hong Kong, and I was the man with the money, I would have my own concerns as to whether the acceptance would be there."[9]
Whether or not Kung Fu was based on a concept by Lee, he was undoubtedly considered for the starring role, according to Herbie Pilato in his 1993 book The Kung Fu Book of Caine: The Complete Guide to TV's First Mystical Eastern Western (pages 3233), and David Carradine himself in a 1989 interview mentions that Bruce Lee was passed over for the role.