Hector Rex is a Motherfucking INQUISITOR LORD of the Ordo Malleus. He carried the title Auditorii Imperator at one point, being badass enough to see the Big E. He is an absolute monster of a human and to top it off, he is a gifted psyker and has a keen political mind when dealing with other factions of the Inquisition. He also carries the title of Lord Proctor in the Scarus Inquisitor Conclave of Eisenhorn and Ravenor fame. It is worth mentioning he defeated AN'GGRATH, you know One of the mightiest Bloodthirsters of Khorne IN CLOSE COMBAT.
...Are we sure Matt Ward didn't make him up?
During Rex's Early years, he was a psyker for the Adeptus Astra Telepathica, basically the psykers who don't get fed into the Golden Throne, or murdered for witchcraft, instead acting as the long range telephone service for the Imperium. Life all things considered for a psyker in the telepathica isn't that bad compared to the other alternatives out there. During his time in the telepathica, he was chosen to undergo genetic modification that turned him into an EIGHT FOOT TALL NON-SPACE MARINE (totally not a space marine because space marines can't be inquisitors *wink wink*). He was recruited into an Inquisitor's retinue and eventually was able to become an Inquisitor himself and then a INQUISITOR LORD. He makes use of the Emperor's tarot constantly. Being a giant psychic not!Space-Marine, this makes him a natural fit for fighting alongside the Grey Knights.
Siege of Vraks
The Siege of Vraks was hell for the Imperium. Vraks itself sat near the fortress world of Cadia and acted as an Armory planet for the Guard forces. It all started when an Ecclesiarchal Cardinal named Xaphan decided to start a holy crusade on Vraks. He rallied the people inciting a war of faith with his trusted advisor Deacon Mamon. This war of faith ended up going a little too far when the Ordo Hereticus decided that he had a little too much power since he was violating the Decree Passive and took it upon themselves to assassinate the Cardinal with a Vindicare Assassin. However the Assassin's bullet failed to kill Xaphan as his Rosarius protected him, and he then rallied the people saying that heretics and traitors were the cause of his assassination attempt (with all those times the Vindicare temple failed to put down targets, one has to ask why does the Imperium even bother with them anymore). This led to Vraks openly rebelling against the Imperium, and the destruction of the local Administratum, Arbites, and Sororitas on the planet. The Munitorum got all pissy and decided to deploy the Death Korps of Krieg to bring the world back into the Imperium's control because of the munitions stored. However surprisingly, Deacon Mamon was actually an Alpha Legion Spy and called backup in the form of the Traitor Legions including Plague Marines, Khorne Berzerkers, AND TRAITOR TITAN LEGIONS.
CUE BIG DADDY'S ARRIVAL
Rex at the consensus of the Scarus Conclave went down with a contingent of Kriegers and Grey Knights including Arvann Stern and wrecked shit on Vraks. Of his accomplishments he personally banished the Khornate Greater Daemon An'ggrath. By the end of the battle, much of the munitions stored on Vraks were used in the fighting on top of the fact that the planet had been corrupted heavily by the influences of Khorne and Nurgle. Rex decided it would be best to put the planet under Malleus Quarantine which caused the Hereticus to throw a bitchfit.
Rex is already a monster of a man and his equipment complements his physique as well. He wears Artificer Armor that has been accommodated to fit his massive bulk. He carries an Anointed Force Sword which he used to banish An'ggrath as well as a storm shield. He also carried a Bolt Pistol that fired PSYCANNON ROUNDS.
However,in his 8th edition incarnation. His bolt pistol fired plain old bolt rounds. Instead the sword Arias is a Force sword that causes an automatic Mortal Wound on any DAEMON that is hit by the weapon, in addition to all other affects.