...C-137. Yes, our Rick. In episode 1, Rick shows up after being away from Beth for a long time. This would be a perfect opportunity for a different dimensional Rick to slip in and take over the family without them aware. Why would he need to do that? Because he fucked up his original Morty, who he probably left to die along with his original family (and unbeknowingst to him, he survived hence the robot parts he has in Season 1).
But that would involve taking out current Morty's Rick. For whatever reason, he probably thought it was best to keep current Morty's Rick alive, because current Morty's true Rick is the evil Rick that died in Season 1, who originally took on the citadel. That Rick, wanting to get his universe's family back after seeing C-137 take it over, probably found a dying Morty on the dimension C-137 left behind and turned him into an android or something, because reasons. Perhaps he knew he wasn't going to live much longer, so his secret weapon was a Morty no single Rick would suspect that would live on after his inevitable death, probably with the AI that nearly replicates his own intelligence.
Oh, and the whole "I finally have taken over the family patriarch!" thing C-137 gets so excited about in S3E1 is probably a dead giveaway that with the citadel destroyed and the galactic federation gone, he has succeeded in sabotaging everybody in his way that would prevent him from going back mentally to the pre-Evil Morty days where he can finally live and bury the fact that he fucked up in the first place.