On the surface, Colonel Simmons came across as a typical government bureaucrat. He led the study of a powerful Ancient space weapon that SG-1 discovered on an alien world, nearly bringing deadly retribution from the Ancients. He also attempted to capture an alien who had taken human form, and who had become enamored with Major Carter. He conducted an investigation of General Hammond and SG-1, submitting a very unfavorable report questioning the team's loyalties and recommending Hammond's dismissal. He was unscrupulous in his methods of gathering information, hacking into the S.G.C. database as "User 4574."
Simmons is a leader at the N.I.D., a civilian organization in the U.S. government, based in Washington, D.C. and assigned to study alien technology and lifeforms that Stargate teams bring back to Earth. He was recruited by Colonel Harold Maybourne. A secret, rogue arm of the N.I.D. operates unscrupulously outside the law, and (after Maybourne's departure) Simmons was for a time at the center of it.
When a wealthy businessman named Adrian Conrad had himself implanted with a Goa'uld symbiote to save his life, Colonel Simmons secretly took him into custody. He used the Goa'uld for its secrets, and eventually hijacked Earth's first interstellar space vessel, Prometheus. While travelling through space, the Goa'uld turned on Simmons and attacked him; Simmons shot and killed the host body, but the Goa'uld took him over. He engaged Teal'c and Jack O'Neill in hand-to-hand combat, and nearly killed the Jaffa before O'Neill sent him out of an airlock to his death.
Ascension - SG-1 meets Frank Simmons, a colonel assigned to the Pentagon who leads an effort to study a deadly alien weapon.
The Fifth Man - Simmons is sent by his superiors to investigate the S.G.C., and threatens General Hammond's command with his negative report.
Desperate Measures - Simmons secretly captures Adrian Conrad, a Goa'ulded wealthy businessman, offering to trade for his knowledge of his race. From the shadows, he shoots Colonel O'Neill to capture the Goa'uld.
48 Hours - Simmons uses the knowledge of his captured Goa'uld to try and blackmail General Hammond, but O'Neill and Maybourne expose him. Simmons is arrested.
Prometheus - Simmons is freed and takes command of the X-303 after a terrorist group seizes control of the ship. But before he can take the ship to a stash of advanced weapons on another planet, the Goa'uld with whom he has been working takes him as a host, and O'Neill pushes him out of an airlock into space.