Thrawn was the main villain of the Star Wars: Rebels animated series. The link below explains things about him, but was a high ranking Empire commander who was a great fighter and military leader.
WookieepediaMitth'raw'nuruodo, born as Kivu'raw'nuru with the core name Vurawn, recognized in his early military career as Mitth'raw'nuru, and better known by his core name Thrawn, was a Chiss male officer of the Chiss Ascendancy and Grand Admiral in the Imperial Navy during the age of the Galactic Empire...
https://starwars.fandom.com/wiki/Mitth%27raw%27nuruodo