Thrawn
Grand Admiral Thrawn (full name Mitth'raw'nuruodo), was a Chiss from the Unknown Regions who was personally elevated by Emperor Palpatine. A noted tactical and strategic genius, he gleaned insights into the psyches of other races by studying their art.
Original EU
He was the commander of the Imperial Remnant's starfleet five years after the death of the Emperor, after returning from an extended mission into the Unknown Regions. He also rebuilt the Empire's military might with the help of the Katana fleet and a set of Spaarti cloning cylinders. Thrawn was well on his way to defeating the New Republic and re-establishing the Galactic Empire before he was assassinated by his Noghri bodyguard Rukh in 9 ABY at the Battle of Bilbringi.
Thrawn was also responsible for seeding the galaxy with sleeper groups of clones, like Jenth-44 on Pakrik Minor (a group of clones made from Baron Fel's genetic material), as well as the establishment of the Empire of the Hand, a group of ex-Imperials, including Baron Fel, and a group of Chiss, whose mission it was to ensure that the galaxy was ready to fight against the oncoming invasion of the Yuzzhan Vong. Ten years after the Thrawn trilogy, their forward base on Nirauan was covertly invaded by Luke Skywalker, R2-D2, Mara Jade and a group of sentient avians, which led to the destruction of Thrawn's clone.
Thrawn's flagship was the Chimaera, captained by Gilad Pellaeon.