- "So you guys are ex-NID. You call yourselves The Trust now, right?"
- —Daniel Jackson
The Trust was an interplanetary terrorist organization based on Earth, composed of rogue ex-NID operatives and the political and business cabal that funded them. Originally, they declared their mandate to be the protection of Earth at all costs, often bringing them into conflict with the teams of Stargate Command. After a failed attempt to exterminate the Goa'uld, the Trust was infiltrated by the symbiotes themselves, and became an anti-alien group dedicated to defending the galaxy from external threats by any means necessary.
When the Stargate program was put into operation in 1997, there was a philosophical skirmish in the government about its mandate. "Some people wanted to make sure that any and all discoveries were brought back regardless of considerations like inter-planetary diplomacy," according to General Hammond. He and his allies disagreed, and their view eventually won out, at least for the moment. However, his opponents did not fall into line; instead, they threw their influence into the NID and pursued their agenda illegally.
Over the next few years, the SGC found itself fighting against extremely well-funded and well-connected NID operations. While they shut down a number of them successfully, they found it nearly impossible to uncover the ringleaders of the conspiracy until 2000, when Colonel O'Neill managed to coerce Harry Maybourne, a captured NID agent, into cooperating with him. The SGC then learned that Senator Kinsey had been the politician pulling the strings of the NID.  He was also connected to a cabal of international business interests known as the Committee, whose goal was to acquire alien technology for financial gain. These members were eventually exposed and arrested with the help of NID Agent Malcolm Barrett. 
After the successful reformation of the NID and the loss of the Committee, its offworld cells reorganized and became more radical both in their methods and their objectives; it was also in this era that they began calling themselves "the Trust." Instead of remaining hidden and operating through the corridors of power as before, their action became bolder and bolder, coming into direct conflict with the SGC and the United States several times. Probably their boldest action was their use of Tok'ra symbiote poison to indiscriminately attack a number of Goa'uld-held worlds in 2004, an action that claimed several Jaffa armies before the SGC and Free Jaffa put a stop to it. 
The Trust was also responsible for trying to personally silence any civilians who grew wise to the existence of alien life, such as Alec Colson, head of Colson Industries, who was attempting to expose the government's secret. Whereas the SGC wanted to quietly clean up the evidence, the Trust turned to outright assassination. Their activities forced Colson to stay at an offworld base for his own protection 
- "They could have brought dozens, maybe even hundreds, of symbiotes back with them. By now, the entire Trust could have been taken over."
- —Samantha Carter
Eventually, however, several agents of the Trust were taken over by Goa'uld, who quickly infiltrated and took command of the entire organization. Under Goa'uld control, the Trust attempted to orchestrate a nuclear war between Russia and America, thus destroying the Tau'ri, so that the System Lords could take the Ancient outpost in Antarctica. This plan is foiled by General Jack O'Neill, Colonel Carter and Russian Colonel Chekov, who exposed the Trust's connections and convinced the Russian president to stand down his forces; they also destroyed the Trust's only Al'kesh bomber, which had remained in Earth's orbit for some time as the organization's base of operations. The ship attempted to destroy the Prometheus, but was destroyed by that ship instead. Presumably the identified Russian Goa'uld agents were arrested and extracted from their hosts by the Tok'ra afterwards.
Despite this setback, the organization remained more powerful than ever; it was eventually revealed (in 2005) that Ba'al was its new leader. The change in leadership and identity did not affect the Trust's mode of operations, however; it continued to infiltrate and occasionally take action against the SGC, the United States, and its allies both on Earth and offworld.
One plan that it attempted to execute was the destruction of Atlantis. The Trust somehow managed to infect Colonel Steven Caldwell with a Goa'uld agent who was assigned the task. Caldwell's Goa'uld managed to rig Atlantis' ZPM to blow when Earth was dialed, and was only prevented by an NID raid of a Trust base which revealed the plan and allowed a warning (ironicaly through Caldwell himself) to prevent it in time. Caldwell's Goa'uld tried repeatedly to destroy Atlantis and had the advantage of not being suspected and the people of Atlantis believing they were looking for a human agent, but he was exposed by Laura Cadman. The Goa'uld completly exposed himself and swore never to give up the needed code, but was tased by Lieutenant Colonel John Sheppard, allowing his host Colonel Caldwell to temporarily regain control of his body and give up the needed code which thrawted the Trust's plan. Afterwards, the Goa'uld agent was extracted by Hermiod with Asgard beaming technology and presumably killed, depriving the Trust of a valuable agent.
The Trust eventually overreached during the Der'kal Invasion, turning the galaxy's citizens against them after their use of the Agent One virus on the Jaffa at Ankgor. With most of its leadership dead, the organization enacted one final plan to align itself with a powerful ally, sparking a crisis over the future of the MBP-305 Jupiter. When the ISGC exposed their part in manipulating China for their own purposes, the Trust agents behind the attempt were hunted down and arrested by the United Nations. The sole surviving member of the group made one last play for power by exploiting a cadre of corrupt politicians within the United States government to take control of Stargate Command. Ultimately, the final operative was brought down by Danielle Talbot and SG-1, and the last remnants of Trust were at last destroyed.