One of the many admirable things about the late Patrick McGoohan is that he came up with a new and unique way of dealing with the problem of every star TV actor (i.e. the problem every other TV actor dreams of having): how to deal with the fact that the public associates you with one role and one role alone. Danger Man, aka Secret Agent, was a popular show on both sides of the ocean and everyone who was likely to watch McGoohan on a new show would immediately think of him as John Drake. Usually there are two ways of dealing with that kind of typecasting: give into it and play only similar roles, or try and break away from it with a different kind of part.
But with The Prisoner, McGoohan combined the two approaches: he played virtually the same character he’d been playing before — one of the many mysteries of The Prisoner is whether this unnamed hero is in fact the same guy from Danger Man — but in a different kind of show. The Prisoner took the goodwill he’d accumulated in his years of playing John Drake, and used it to cajole the audience into going along with something they hadn’t seen on TV before. (Though they’d seen it in movies before, and plenty of it; The Prisoner was the TV show that finally incorporated the cryptic dialogue and even more cryptic storytelling of the movies and plays of that era.) And he looked at some of the things he’d been doing on his previous show, but from a different angle, and without doing a sequel or a rehash of the previous show. Few stars have been able to pull that off; one of the few is Clint Eastwood, who has made a second career out of creating thinly disguised elderly versions of his most popular roles.
I actually think Danger Man is a more satisfying series than The Prisoner, but the point is not that The Prisoner made the earlier show obsolete, but that it built on it and did something new.