Sergeant Sylvester Sly Siler (Dan Shea) is a Master Sergeant in the United States Air Force and one of Stargate Command's primary technicians and engineers. He has been a vital part of base operations since the inception of the Stargate Program. At the first possible sign of any Stargate malfunctions at the base, Siler is always on the scene. He is an expert in promptly recharging each individual chevron to its proper power output and activating the Stargate from the central command main computer. He is also responsible for all key functions and can bypass the main programming system if a crisis occurs. Siler is also the maintenance engineer for the Alpha Site, making sure that the SGC have immediate access to the base in the event of a potentially devastating alien attack on Earth. He is accident prone and often injured during the course of his work.