Rick's clone is a minor character appeared on the episode Mort: Ragnarick and is one of of Rick Sanchez's clone bodies.
In "Mort: Ragnarick", he was the original way for Rick to exit Valhalla. Similar to how Operation Phoenix works, when Rick was done building a device to harness Valhalla's infinite energy, Morty was supposed to push a button to upload Rick's consciousness into the clone so that he could come back to life again. However, this plan was thwarted when Bigfoot tricked Morty and murdered him as well. With no one left to defend Rick's backup clone, Bigfoot broke his capsule with clear murderous intent. However, this activated some sort of precautionarily-installed emergency protocol that caused the clone to wake up and flee.
The clone does not talk, but incoherently babbles as it runs, burrows and climbs away, doing whatever it can to stay alive. Throughout the episode, the Pope uses this to his advantage by employing him as bait in order to train Bigfoot as a weapon for the Vatican.
In the episode's post-credit scene, it was revealed that this babbling clone had become the new Pope, much to the old Pope's horror. While it isn't shown how this came to be, it's most likely the work of one of Rick's shenanigans, seeing how it would be very in-character for him to do something like that.
Clone Rick (or Pope Rick), as of yet, hasn't made an appearance in any episodes other than the one in which he was introduced.