A civilian branch of the United States government, which appears to have a significant military component. The agency is devoted to the protection of Earth, and thus works with -- and often comes into conflict with -- Stargate Command.
The N.I.D. is plagued by a rogue group within its ranks, which operates outside the law to acquired advanced alien technologies by any means necessary. This has included use of Earth's second Stargate for covert, off-world operations, placing a mole within the S.G.C., blackmailing General George Hammond, and stealing alien technology from Area 51.
Thanks to the efforts of agents like Malcolm Barrett, the N.I.D. is now a reformed agency committed to civilian oversight of military programs. Another of its most prominent agents was Richard Woolsey, before he joined the I.O.A.
Members of the rogue N.I.D. include (or have included):
Keffler (possibly hired)
Makepeace (a mole, possibly hired)
Some members have served in both camps.
After the N.I.D. was purged of its rogue elements, the movement eventually became known as the Trust.
Enigma - Colonel Maybourne arrives at the S.G.C. to try and forcibly take a group of Tollan refugees -- who possess advanced technology and knowledge -- into N.I.D. custody.
Bane - With little concern for Teal'c's life, Maybourne takes him into custody after Teal'c is stung by an alien insect, and begins a terrifying transformation.
Touchstone - A rogue N.I.D. team uses Earth's second Stargate to steal an advanced weather-control device from another world.
Shades of Grey - Maybourne recruits Colonel O'Neill into his rogue operation, but Jack turns on him and brings the off-world N.I.D. team to justice -- and exposes Colonel Makepeace as an inside operative.
Chain Reaction - A shadow group, apparently behind the rogue arm of the N.I.D., blackmails General Hammond into retiring, so that they can place someone more sympathetic to their philosophy into command at the S.G.C. O'Neill and Maybourne discover that Senator Kinsey is linked to them.
Ascension - The N.I.D.'s Colonel Frank Simmons tries to take into custody an alien who has followed Carter back to Earth, while activating a powerful weapon found on Orlin's planet.
The Fifth Man - Colonel Simmons investigates the S.G.C. and SG-1, calling into question their loyalty and trustworthiness.
Desperate Measures - Revealing that his motives are not on the up-and-up, Simmons takes a Goa'ulded millionaire named Adrian Conrad into custody for some future purpose.
Wormhole X-Treme! - SG-1 tracks an alien ship moving toward Earth, only to discover that the N.I.D. knows about it and is carefully watching its owners with the intent of seizing the vessel.
48 Hours - Frank Simmons is arrested when SG-1 learns that he has the Goa'ulded Adrian Conrad in custody, and is using his knowledge for blackmail.
The Sentinel - SG-1 brings two former rogue N.I.D. officers on a mission to repair an alien device they once broke -- the only thing that can protect a peaceful world from Goa'uld occupation.
Nightwalkers - SG-1 investigates strange happenings in a small Oregon town, and finds that the N.I.D. is keeping tabs on the town -- whose Goa'ulded inhabitants are building a ship.
Prometheus - When a rogue N.I.D. team hijacks the X-303, Frank Simmons assumes command, and brings Adrian Conrad on board to make the ship's new hyperdrive functional. Both men are killed as they turn on each other.
Smoke and Mirrors - SG-1 exposes the Committee, the shadow group behind the rogue N.I.D. operations, after they use alien mimetic technology to try and assassinate Senator Kinsey and frame Jack O'Neill.
Disclosure - Senator Kinsey attempts to convince the international community to give the N.I.D. direct control over the Stargate program -- and almost succeeds.
Resurrection - Agent Barrett calls SG-1 to a recently discovered rogue N.I.D. research facility in L.A., where a scientist named Keffler has succeeded in creating a Goa'uld-human hybrid.