He helped Doctors Ignatio Moebius and Elena Petrova while they worked on Project ReGenesis. After GDI Commando Captain Nick "Havoc" Parker rescued Moebius and killed General Gideon Raveshaw, the Tiberium mutants mutated rose up and battled Nod, and Schuman was in the middle of the fight.
He was apparently taking a break when it began, and was wounded. He left the break room (and left his security key too) and hid in his office as the mutants killed other technicians that were not as fast as Schuman.
When Havoc and Mobius come through and kill the mutants in the lab, Schuman is elated to see Mobius still alive. He shows them the way to his security card as they need it, then stays down in the Nod base.
Schuman appears only in Renegade.