Bryce is a human general in the United States military at presumably Area 51 in Nevada. He has seen Optimus Prime first hand while debriefing William Fowler. As a General of the United States military, he is in charge of military operations at Area 51 and relies on field reports from Fowler to determine the allegiance of the Autobots to human-kind.
Following an attack on Alden Military Base, Agent Fowler tried unsuccessfully to convince General Bryce by phone that the Autobots weren't behind the attack, and Bryce told him that the military are under orders to shoot any Autobots on sight.
General Bryce had Private Daley film via camcorder as Fowler came in for a debriefing to explain Optimus Prime's recent supposed death, and Fowler again tried to explain that the body the military had in storage was Nemesis Prime, a clone created by MECH. After more explanation from Fowler about Optimus and the other Autobots, during which Bryce almost had the agent submitted to a psych evaluation after he misheard "Unicron" as "unicorn", Fowler soon had Optimus appear and speak to Bryce himself, and the general was convinced of Prime's loyalty and good health.
Following the establishment of a Decepticon fortress near Jasper, Bryce told Fowler that the generals were itching to nuke the site. Bryce called Fowler in for another grilling when the Decepticons started raiding human technology again.