One of the unnamed combatants seen in the Imperium of Man trailer carries a shotgun. Very little is know about him.
Speculative/What is it? Edit
1. Adeptus Arbites. Edit
The Adeptus Arbites are high standing members of the Imperium's police force. They are callus and ruthless; unforgiving to the those criminals condemned by Imperial law.
The Adeptus Arbites were first introduced in the Warhammer 40,000 RPG Rogue Trader and it's expansion Dark Heresy. They are offered a background and weapons set up for the player character, his family or his team. They use Shotguns almost exclusively; the class has only been seen to use shotguns.
The images shown in the game trailers and screenshots strongly resemble the original images of the Adeptus Arbites.
2. Imperial High Officer Edit
The soldiers uniform is not unlike that of a high standing Imperial Officer. They too are known to use shotguns albeit not as exclusively as the Adeptus Arbites.
3. Inquisitor Edit
In a interview Danny Bilson was asked: "What does being an Inquisitor mean?" he replied "That's down the road somewhere. I always say too much in these things, but I get excited.". If the Inquisitor is class he is almost definitely this class as none of the other classes look like one.
A issue with this theory is that Inquisitors always have the "I" of the Inquisition on there armour. If the class really is a Inquisitor, it is possible that the versions seen so far are acolytes, a Inquisitors in training.