One of Gerry Anderson's only non-science fiction efforts, and his first since Crossroads to Crime (1960).
The lead role was originally named Craig Bradford and Chuck Connors was the first choice before Robert Vaughn was cast and the character renamed Harry Rule.
Character actor Nigel Green made one of his last appearances on TV when he was a guest star on "The Protectors." Not long after, this underrated actor died tragically in May 1972.
Robert Vaughn enjoyed spending time in England whilst making the series. He stated that London was a favourite city of his.
Actor Derren Nesbitt nearly vanished from the acting scene not long after he appeared in two episodes of the show. 1973 saw his career being damaged by scandal.