Sierra 092 - Jerome, Leader of Red Team, who appeared in Halo Wars.
Though he is supposed to be a Sniper class, and normally carries a Spartan Laser... In all the cinema scenes he used a shotgun. Though I suppose it doesn;t matter much, as Spartans are proficient with all types of arms.
He is supposed to have the spartan helmet design on his right shoulder armor... but I couldn't get it to look very good, so I left it out. Either way he is marked more notably by the red on his armor.