Gaunt was born on Manzipor, the son of an officer of the Jantine Patricians. His father was killed fighting Orks, betrayed by a superior who abandoned his post in fear, and the orphaned boy was sent to be raised and schooled at a Schola Progenium, where the Imperium turns the children of its fallen servants into instruments of its will.
He came of age in the harness of a commissar. Serving as a cadet under the veteran Commissar Oktar and attached to the Hyrkan regiments, he learned his trade in war zone after war zone, and was raised to full commissar at his mentor's deathbed. It was during the opening of the Sabbat Worlds Crusade that he caught the eye of Warmaster Slaydo himself. When Slaydo fell at the pivotal battle of Balhaut, he granted Gaunt a rare deathbed promotion to the unusual rank of Colonel-Commissar, uniting military command with the commissar's authority in a single man.
Gaunt was meant to lead three regiments raised from the forested frontier world of Tanith, but disaster struck during their very founding, and the world was lost with only enough survivors to form one battered regiment. He forged those ragtag, under-equipped men into the Tanith First-and-Only, a peerless force of scouts and marksmen who fight in distinctive camo-cloaks and carry the straight silver war-knives unique to their people. Masters of stealth, infiltration and the reconnaissance raid, they win the impossible missions that break other units.
What sets Gaunt apart from his grim brethren is his devotion to the men under him. Where most commissars rule by fear and the summary execution, he earns loyalty by spending it back, protecting his Ghosts and valuing their lives. That bond carried him and them through the length of the Sabbat Worlds Crusade, and Gaunt would rise at last to the exalted rank of First Lord Executor, the right hand and acknowledged successor of the Warmaster Macaroth.