Grodin Tierce was a male Human who held the position of Royal Guard. During the events of the Thrawn campaign, the Grand Admiral cloned him as part of an initiative focused on developing enhanced soldiers. He passed away not long after this. His clone later participated in a campaign aimed at overthrowing the New Republic, but was killed in 19 ABY.
Like all individuals who became Royal Guards, Tierce began his military service as a Stormtrooper. Identified as TR-889, Tierce reportedly distinguished himself as an exceptional soldier and was selected for Royal Guard training on the planet Yinchorr.
In 4 ABY, Tierce was assigned to a Stormtrooper unit on Magagran engaged in combat with a rebel group. The practice of periodically rotating Royal Guards back into the ranks of the Stormtrooper Corps proved crucial for Tierce when a significant number of Royal Guards were killed during the destruction of the second Death Star.
Sometime after the death of Palpatine, Tierce served as a Stormtrooper officer under Grand Admiral Thrawn on the Star Destroyer Chimaera. Thrawn, impressed by Tierce's combat abilities and physical strength, chose Tierce as the basis for a new type of clone two months prior to the Battle of Bilbringi in 9 ABY. Tierce felt responsible for Thrawn's demise. He had positioned the majority of his forces near the Chimaera's hangars, anticipating that any attempt on Thrawn's life would originate from a commando team landing in those areas during a battle. Instead, Thrawn was assassinated by Rukh after the Noghri discovered the Empire's betrayal of them. Tierce supposedly killed Rukh as he fled. Tierce subsequently died on Generis not long after these events.
According to "Specter of the Past" and the Databank entry for Rukh on StarWars.com, Tierce assassinated the Noghri after he assassinated Thrawn. However, in Vision of the Future, it is stated that Tierce died during the assault on Generis, which occurred before Thrawn's death. It is possible that his clone led the squad.
The Essential Reader's Companion contains a misspelling of Tierce's first name, rendering it as "Grodon."