The pilot for the original Star Trek series was shown to NBC executives in 1965 — they rejected it, so Gene Roddenberry made a different pilot, which they liked much more. The very first Trek pilot that ever boldly went (titled "The Cage") had no Captain Kirk in sight — Jeffrey Hunter played Captain Christopher Pike, and Majel Barrett played his first officer, referred to only as "Number One." Others have been called this name over the years (Commander Riker on Star Trek: The Next Generation, most notably), but 54 years later, the original Number One is finally ready to boldly go once more.
https://www.syfy.com/syfywire/original-number-one-star-trek-discovery