The original Grodin Tierce was one of the finest combat stormtroopers ever to serve the Empire. His successes raised him to command rank far more quickly than even stormtropper norm. At the age of twenty-four he was selected to serve the Emperor as one of the elite Royal Guard. His fierce loyalty to Palpatine's New Order was second to none. He died in combat as part of a stormtrooper unit involved in Thrawn's campaign against Generis.
This was taken directly from Vision of the Future.
The Grodin Tierce in Specter of the Past and Vision of the Future is actually a clone. It was an experiment by Grand Admiral Thrawn, to create a class of warlords who combined Thrawn's own military and tactical genius with the combat strength of a stormtrooper.
However, the experiment was a failure and was abandoned. Instead of a tactically brilliant leader, he got a tactically brilliant stormtrooper; someone who was only capable of manipulation, someone who had no vision. He was killed by Shada D'ukal on the bridge of the Star Destroyer Relentless.