Sebastian Yarrick, the "Hero of Hades Hive," is a commissar of the Officio Prefectus, famous for his involvement in the Second and Third Wars for Armageddon in the last century of the 41st Millennium. There he fought against the forces of the Ork Warlord Ghazghkull Mag Uruk Thraka.

Yarrick was already old when the war began and was scheduled to retire on the day the Greenskins landed. He possessed an excellent history serving with Armageddon's Planetary Defence Forces and a reputation for unswerving loyalty to the Emperor.

In his youth he had learned the Ork language from a human raider captured by the savage xenos and was one of the few recognised experts in the Imperium on Ork psychology and culture.