In all of Star Trek, few aliens are mentioned as frequently -- with as little screen time -- as Rigellians. First mentioned in the TOS episode, "Journey to Babel," referring to their similar physiology to Vulcans, Rigellians weren't seen in the franchise until one was listed as a background character in Star Trek: The Motion Picture. In fact, the idea of what a Rigellian is has become rather convoluted over the years, as different versions have shown up or been referred to from one series to the next. One Trek series could solve the riddle of who, or what, the Rigellians are.
Source：https://www.cbr.com/star-trek-strange-new-worlds-rigellains-explained/
