Long ago, back in 1994, there was a little film starring Kurt Russell an James Spader called Stargate. It sparked a lot of people's imaginations, and even did pretty well for itself. So of course people started wondering about a big-screen sequel. But instead of a big-screen continuation, we got Stargate: SG-1 in 1997 on Showtime. The series picked up events about a year after the film, but did so without the involvement of the film's writers Dean Devlin and Roland Emmerich.
To say it turned into a successful franchise would be an understatement. SG-1 lasted ten years, Stargate: Atlantis notched another five, and Stargate Universe just premiered to huge ratings for Syfy. Add to that the various telefilms that have been filmed, including a forthcoming continuation of the Atlantis saga, and you've got yourself one of the most successful sci-fi franchises of all time.