Did you know that the word 'protagonist' has Greek origins and literally means 'first contestant' or 'first character'?
Accordingly, there can only be one protagonist in a play or story, and it is the character who first appears. Therefore, when a novel is related in the first person, the protagonist is always the narrator, even if he/she is not the main character.
'Protagonist' has come to mean 'main character', and people often refer to multiple 'protagonists'. But if 'protagonist' is simply a major character, what name do we give to the character who first appears? Does it even matter?
It's nitpicking, I know, but the stickler in me wants a distinction. Do you?