Star Trek: Strange New Worlds made a bold choice for the Enterprise's Chief Medical Officer. Instead of creating a brand-new character for the prequel series, the show's creators decided to pluck an obscure character from Star Trek: The Original Series. Introduced in The Original Series, Season 2, Episode 16,"A Private Little War" as an expert in Vulcan medicine, Dr. Joseph M'Benga would later appear as the CMO aboard the Enterprise in Strange New Worlds. So, where had he been in the intervening years between Pike and Kirk's command, and why wasn't he the ship's doctor during those later voyages?
Source：https://www.cbr.com/strange-new-worlds-mbenga-star-trek-tos-absence/
