Here are some facts to support this idea:
1. Spock was the first character Roddenberry created for Star Trek after getting the obligatory “Number One” character of out of the way, which he conceived to fulfil a promised he made to his mistress and future wife that she’d be a part of his next series.
Source, please? I haven't heard that before, and it sounds unlikely. We know that Roddenberry was inspired by the Horatio Hornblower novels, so it seems likely that the first character he conceived was the captain (although it took him a long time to settle on a name).
A lot has been written about the development and production of ST, but I can't recall reading anything about Roddenberry's earliest creative process before the original 1964 pitch document, which lists multiple characters including Captain April (later Pike), Number One, Jose Ortegas (later Tyler), Dr. Boyce, the "probably half-Martian" first lieutenant Spock, and Yeoman Colt, in that order. Note that Spock is second-last in the list, hardly the position you'd expect to find the lead character.
According to Majel Barrett
, the first character introduced in the [Cage] script was Number One. "That was the first character Gene wrote into the script,
" Barrett stated. "Captain April was not an afterthought because he knew he had to have a captain, but the first character that was described was Number One.
" (Star Trek Monthly issue 27
, p. 43)
As promised, when I came across the evidence to support my claim, I'd post it immediately. 1 down, 1 to go . . .