Actual Air Force Chief of Staff Michael E. Ryan

From the Stargate Wiki:

This episode marks the appearance of General Michael E. Ryan, the actual Air Force Chief of Staff at the time, playing himself. He is not a character on Stargate SG-1 created by writers, but a real General in the real American Air Force in the position of Air Force Chief of Staff. This appearance is part of a long running participation by the real American Air Force due to the positive way it has been portrayed on the show and will be for the next 5+ seasons.