@Natsuki151 He does indeed appear in "Rebels". But that's not his first appearance.

If you are interested in checking out other SW-media like novels, I'd recommend you to give the Legends Thrawn-trilogy a try, written by Timothy Zahn, starting with "Heir to the Empire". Not only is it the source of Thrawn's first appearance, it's generally an excellent trilogy. The story takes place a couple of years after Return of the Jedi and is basically about the New Republic (which would be the new government after the fall of the Empire) trying to stabilize itself and maintain peace while new threats arise. The whole trilogy is well written, portrays already established characters very accurately (Luke, Leia, Han, etc.) and introduces several interesting new characters.

These three books are actually my favorite SW-books and they are generally very popular; I don't think I've ever come across somebody who didn't like this trilogy. They are also the reason why Thrawn is one of my favorite SW-characters. So, I'd definitely recommend you to give this trilogy a try if you're interested in reading SW-novels

The most impressive thing his people do at least is that they'll infiltrate every influential/major faction in the galaxy (the old republic, the old sith empire, the new republic, the galactic empire, and the Jedi). This allowed Thrawn's people to gain power through information against his foes.

He's an excellent strategists and he's CERTAINLY handsome

He’s a master at anticipating the rebels strategies and maneuvers. On top of that he’s essentially the saving grace for the empire in Rebels because let’s be honest they were a bunch of dim wits before Thrawn made them seem slightly competent.

The man is a genius and looks awesome in white - even after Labor Day.

He's actually good at naval warfare, and unlike most Imperial officers, he's not overconfident. With a force user, you know they'll lose, but Thrawn is a lot harder to beat. I also find his character really interesting, especially his relationships with Thrass, Eli, and Nightswan. He has good intentions, but you never know how far he'll go

He was a sinister villain in Rebels season 3 and 4

He was also a good commander leading his army to victory

In addition he is a skilled fighter

I also thought Lars Mikkelsen did a great job with the portrayal

I am interested to see him in Ahsoka

I really like the whole character, his ethics, intellect - and particularly how his logic seems so confusing but if you ‘crack’ his ideas it makes perfect sense. His interactions in the ascendancy trilogy are particularly interesting.

I could turn this into a book

He makes art history dangerous.