Despite being the definitive version of Star Trek for a generation, Star Trek: The Next Generation was never supposed to work. Conventional wisdom suggested that no reboot ever compared to the original TV series -- either in quality or ratings. However, Gene Roddenberry had been through it all with Paramount before. In fact, The Next Generation was largely assembled from leftover pieces of a cancelled show called Star Trek: Phase II.
Source：https://www.cbr.com/the-next-generation-assembled-star-trek-phase2-leftovers/
