Decimus is voiced by Kirk Thorton.
Decimus was responsible for the design and mass-production of lethal toxins that were to be pumped into New Madrid's massive Terraforming Tower, releasing the toxins into the planet's atmosphere which would kill millions of civilians planetwide. However, he and his toxin stores were eventually intercepted by the 8th Armored Division's 1st Recon Platoon in a secret Spear laboratory complex on New Madrid.
In the intense skirmishes that followed, Decimus's entire store of toxins were destroyed and he himself was killed by 1st Recon, thus ending his toxin threats.
- Decimus wore an enhanced version of the armor worn by the Spear's elite Crimson Guard units. This grants him greater reserves of shielding and armor compared to other infantry units, and he is fought in gameplay as a minor boss. His weaponry included a Missile Launcher firing Napalm Missiles, a Shotgun firing Concussion shells, and his grenades are apparently filled with the same niacin derivative toxins contained in his mission critical caches.
- Though it is presumed that Decimus held very high rank in Orion's Spear as he is seen taking orders solely from General Salvador in person and was entrusted with the toxins critical to Salvador's plans, he is seen wearing only Sergeant's Pauldrons in cutscenes. However, his actual rank is presumed to be higher than Captain as he was seen giving orders to them in his final battle, and is shown to be wearing Captain's Pauldrons during gameplay.