I know I've seen someone post that they though Evil Morty is a Rick but I noticed something after seeing the ending of the citadel episode again that I hadn't noticed before and I think it's kind of obvious watching it now. Evil Morty's speech pattern is very similar to Rick's after listening to how he was speaking and he actually sounded nothing like a Morty would sound. He sounds like a Rick in a Morty's body when he does his monologue at the end of the episode complete with Rick's overall condescending tone when he speaks and his mannerisms when he's on top of the world. We also know he figured out how to zap his consciousness into other bodies and that he's old as shit and a huge prick who would actually do this. We're also probably never going to find out because Rick said the Citadel probably won't have any bearing on his life ever again, the president in the season finale is actually the President of the US, and also because we probably won't get another season for a couple of years and Rick and Morty still have to find that szechuan sauce.