David Carradine had no formal martial arts training of any sort. He had received some training as a dancer when he was younger. This was a particularly aggravating fact for Bruce Lee after he was turned down for the part of Caine.
The set for the Shaolin Temple was originally a set used for Camelot (1967) that was inexpensively and effectively converted for the Chinese setting.
John Saxon was offered the role of Caine, but was unable to do it. Instead, he appeared in Season 1, Episode 1, "King of the Mountain".
According to Bruce Lee's widow, Linda Lee Cadwell, Lee originated the concept, and was intended to star in the series, but David Carradine was cast because the network felt the American audience was not ready for an Asian actor as the lead, and Lee received no credit for his concept (this was dramatized in Dragon: The Bruce Lee Story (1993)). However, according to the producers, although Lee was consulted and was considered for the role, they created the concept and Carradine was always their first choice.
According to Matthew E. Polly's authoritative Bruce Lee biography, Fred Weintraub's memoir, and the synthesis article "The Truth about the Creation of the Kung Fu Series" (Martial Journal), Bruce Lee was not the creator of this series.
Ed Spielman invented the character, and the movie treatment he wrote with Howard Friedlander in 1969 was the origin of the show. Warner Brothers first rejected the movie script for development, and later produced the television version. Bruce Lee (among others) auditioned for the part of Caine, but the studio was reluctant to hire a Chinese actor, had concerns with his accent, and considered that his intense personality wasn't fit for the role.
In October 1971, a month before Warner Brothers officially designated David Carradine for the role of Caine, Warner Brothers executive Ted Ashley offered Bruce Lee an exclusive development deal to create his own TV program. Bruce Lee's treatment described a show called Ah Sahm, which he later retitled The Warrior. Lee did not sign Ashley's deal, preferring to see how The Big Boss performed in theaters. When that movie was a success, he abandoned his plans to be a TV star and instead focused on movies.