In John 1, John the Baptist said he was not the Christ, not the Prophet, and not whom?

Answer: Elijah

Asked by priests and Levites, John denied being the Christ, Elijah, or the Prophet.

“And this was John’s testimony when the Jews of Jerusalem sent priests and Levites to ask him, “Who are you?” He did not refuse to confess, but openly declared, “I am not the Christ.” “Then who are you?” they inquired. “Are you Elijah?” He said, “I am not.” “Are you the Prophet?” He answered, “No.””— John 1:19-21 (BSB)