Grand Admiral Thrawn was a Chiss, a species of aliens that lived in the Unknown Regions. He was a brilliant military strategist and commanded the remnants of the Imperial Fleet in a series of stunning victories against the New Republic.
Grand Admiral Thrawn is described as a tall, solidly built humanoid with blue skin and piercing red eyes. He was the only non-human to ever reach the rank of Grand Admiral in the Imperial Navy. As a Grand Admrial, he wore a white uniform. This is seen as a departure from the standard charcoal grey or olive colored uniforms that Imperial officers wore as shown in the classic Star Wars Trilogy, although there is a white-uniformed officer on the Death Star in the first film.
Thrawn was assassinated at the end of "The Last Command", the final novel in the Zahn trilogy. His bodyguard, Ruhk, discovered the oppression that Thrawn had put his race under and took vengeance against him, stabbing him aboard his flagship in the middle of a climatic battle. Thrawn's last words were simply "But it was so artistically done."