Commander Jacobus is a turian mercenary and a subordinate of Saren Arterius. He was in charge of searching for Prothean artifacts buried on an unidentified ice planet in the Crescent Nebula.

When Tali'Zorah nar Rayya and Keenah'Breizh land on the planet to investigate the geth presence, Jacobus learns of their intrusion and immediately attempts to kill them, knowing that if he fails Saren will kill him and his team. Jacobus pursues the quarians to Illium, where he is able to land first and set up an ambush while the quarians are barred from docking. He and his mercs kill the quarian crew of ship Honorata, but Tali and Keenah escape and stow away on a transport ship bound for the Citadel. Relentlessly, Jacobus tracks the two quarians down and chases them across the Citadel, wounding Tali and Keenah. He corners them in an incinerator, where Keenah has already succumbed to his wounds, but Tali springs a trap and seals Jacobus in the incinerator as she activates it. Jacobus is obliterated.