Rick

Rick was first mentioned by Roy in multiverse travel 2, but he appears for the first time in home alone.

The remote
One theory made by the dude who made the freakin character says that the remote Sonic finds used to belong to Rick. This is confirmed in a deleted scene of the opening to Multiverse Travel 2 where Roy mentions that they stole Rick’s portal gun.

In others shows
He is also mentioned multiple times in Adventures of Roy, and had his own show called adventures of Rick and Morty, which was canceled in 2019.