Sergeant was the warrior trainer of Durnholde Keep, in the Hillsbrad Foothills. The real name of "Sergeant" is unknown, but he is described as "huge by human standards", easily over six feet tall. He had red hair, with a long beard, a barrel-chest and wore a black scarf and an earring in his left ear. Although a tough seasoned fighter, he let his recruits know who was in charge, but also kept a sense of compassion for them.
He was the trainer of Thrall, after Aedalas Blackmoore found him next to his murdered father (Durotan) and mother (Draka), along with one of Orgrim Doomhammer's traitorous guards. On the first day of training with Thrall and his other recruits, Sergeant said that the earring he wore had not been removed for thirteen years, and that with each group of recruits he issued a challenge to rip the ring out of his ear. If a recruit were to do so, he would allow them to beat him to a pulp. Thrall knocked Sergeant to the ground and in his 
[Bloodlust] nearly snapped his neck in a duel. This was the closest any of his recruits ever came to removing the earring.
Many years passed on and Thrall stayed in training with Sergeant, even though all the other recruits passed on in the ranks. Sergeant had the idea of setting up a scenario for training where the human recruits were in the position of human soldiers, armed with real weapons, coming across a wild Orc and Thrall was obviously cast as the wild Orc, only armed with a wooden sword. During one of these drills a transport wagon of captive Orcs went by the courtyard where they were training. At the sight of Thrall (also Thrall's first real sighting of another Orc) one of the Orc prisoners broke free and charged towards Thrall. Sergeant ordered the recruits to turn their weapons onto the loose Orc and Sergeant helped kill it. After that event Sergeant was in hot water with Blackmoore who blamed him for Thrall seeing another Orc for the first time. Sergeant later tried talking Blackmoore out of putting Thrall into nine gladiator battles in a row, a feat never done before, but Blackmoore didn't listen to Sergeants advice. Thrall lost the last fight, against an Ogre, after which he was abused by Blackmoore and other men who had lost money betting on him. Sergeant came in and got them off of Thrall and stayed till the healers came, at which point he told Thrall that Blackmoore should have been proud of him, and apologized for the way he acted. Thrall escaped Durnholde Keep after the events of that night, and later attributed his knowledge of honor and mercy to Sergeant.
Thrall returned to Durnholde with Grom Hellscream and an army of Orcs and demanded the release of the Orcs in the Internment Camps. Sergeant tried to talk Blackmoore out of going to battle with the Orcs because he knew the humans would lose. Blackmoore then threw the severed head of Taretha Foxton at Thrall's feet, which enraged Thrall, at which point there was no turning back for the battle that was about to ensue. Sergeant was repulsed by what Blackmoore did but had no option but that to scream the order to start cannon fire on the Orcs. With the realization Blackmoore had gone insane, Langston was second in command, but when questioned about what to do next, he couldn't come up with an answer, so Sergeant took command of Durnholde and the troops. Thrall killed Blackmoore and went and found Sergeant and his troops, who were stuck in a stand-off with an Orc troop. Sergeant was promised that he and his men, and also everyone else in the city would walk away alive if he and his troops put down their weapons and stopped fighting. They put down their weapons, and then left the city, which Thrall then destroyed with his Shaman powers.
It is unknown what became of him after the Battle of Durneholde.
For more information check out Lord of the Clans (Warcraft Book #2) written by Christie Golden.