Leader of the Imperial Remnant. Wants to study Baby Yoda's blood for unknown reasons. Maybe he is behind the Snoke clones found by Kylo Ren on Exegol? Very likely has strong ties to the Sith Eternal cultists. Heck, maybe he even knows that Palpatine cheated death by transferring his consciousness into a clone body. He seems to know a lot about Mandalorian culture. Actually, he knows EVERYTHING about EVERYONE and EVERYTHING. Defeated by Din Djarin in combat. We'll have to wait until season 3 of the Mandalorian to learn more about him.
Moff Gideon didn't appear until, like, the end of season one. That's how much of a mystery he is! Long live the Empire.