In the Star Wars Legends continuity, Grand Admiral Thrawn dies at the hands of his bodyguard Rukh on the planet Nirauan. Rukh stabs Thrawn during a confrontation that ends with Thrawn being killed by his own bodyguard.

Thrawn died during the climactic Battle of Bilbringi at the hands of his Noghri bodyguard, Rukh, who had discovered the duplicitous oppression of Honoghr for which Thrawn was responsible. Rukh crept up behind Thrawn as he was sitting in his command chair and stabbed him through the chest from behind the chair.

lightsabers, the force, grand admiral thrawn, boba fett, the emperor and Darth Vader. star wars rules

It was a New Republic victory despite heavy losses. Throughout most of the battle it actually looked like a pretty clear Imperial/Thrawn victory until Grand Admiral Thrawn was assassinated by his own bodyguard.

Without Thrawn his second-in-command and successor (Gilad Pellaeon) lost hope and ordered a retreat, so the Bilbringi shipyards were occupied by the New Republic

The corresponding naval ranks are normally fleet admiral, grand admiral or admiral of the fleet.