Osvald Teshik is a human Grand Admiral from Anaxes, one of the twelve officers Palpatine elevated to the new rank in 2 BBY. He is a Star Wars Legends character, introduced in the West End Games roleplaying supplement The Far Orbit Project (1998).
The punishment
Teshik commanded the Imperial Center Oversector — the core of the galaxy — and in 0 ABY he failed to capture the defecting frigate Far Orbit. Palpatine's response was a suicide assignment: attack the Hapes Consortium with a force plainly inadequate to the job. At the Battle of Andalia the Hapan navy destroyed his fleet and left him so badly injured that roughly seventy-five per cent of his body had to be replaced with cybernetics.
Endor
Four years later he commanded the Star Destroyer Eleemosynary in the defence of the second Death Star. When the other Grand Admirals present withdrew, Teshik stayed and fought on for another four hours until ion cannon fire disabled his ship. He was captured, tried by the Rebel Alliance for war crimes, and executed.
Why he is worth knowing
Because he is the counter-example inside the Circle of Twelve. Most of the Grand Admirals responded to the Emperor's death by declaring themselves emperor, defecting, or flying into a star. Teshik — mutilated on the Emperor's orders, and fully aware of it — was the one who kept firing.