Paul Gertz, one of the head writers on the show has said that the extent of Gene Roddenberry's involvement in the creation of the show was a premise written on a napkin in a lockbox full of obscure notes written on things like receipts, scraps of paper. Out of that small note, they created the show.
The show is famous for the unusually high turnover rate among the regular cast, partially due to contractual disagreements between the cast and the producers. Almost all of the show's major characters were killed or otherwise removed within a season or two of being introduced. In fact, the only character to appear as a regular during all five seasons was FBI Agent Ronald Sandoval (Von Flores), the show's main antagonist.
During the filming of the series occasional sights of the World Trade Center in New York City can be seen. As the series is set sometime in the first couple of decades of the 21st Century, it's interesting to see a building which, by the projected time the series was set in, was no longer there.
After Star Trek was cancelled back in 1969, Gene Rodenberry began work on new sci fi shows among which included this series. Twentieth Centuary Fox were interested in developing the pilot in the late 70's but Gene became busy with the Star Trek movies as well as Star Trek: The Next Generation.