The Trust is an interplanetary terrorist group based on Earth, composed of ex-Rogue NID operatives and ex-Committee members and later Goa'uld who took control of numerous Trust operatives after the downfall of the Goa'uld Empire, giving the Goa'uld a stronghold and also granting them knowledge about the inner workings of the various governments of the major countries of Earth.
The Trust are considered personal enemies of both the SGC and the NID due to the fact that the Trust and its agency operate outside the rules, willing to do anything in their power to stop any possible foes from attacking Earth. Agents of the Trust believe they have the right to use anything necessary to protect and defend Earth. They often show little to no concern for the number of innocent lives that will be lost as a result of their actions.
When the Stargate Program began operating in February 1997, a philosophical skirmish in the government about its mandate arose. According to Major General George S. Hammond, the Commander for Stargate Command, some unnamed people wanted to ensure that all discoveries found on numerous alien worlds were brought back regardless of taking into account matters like inter-planetary diplomacy. Hammond and his allies strongly 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, vowing to obtain alien technology at all costs. (SG1: "Touchstone", "Shades of Grey")
Over the next few years, Stargate Command found itself fighting against extremely well-funded and well-connected NID operations. While they shut down a number of the cells successfully, they found it nearly impossible to uncover the main ringleaders of the conspiracy until 2000, when Colonel Jack O'Neill managed to coerce Colonel Harold Maybourne, a captured NID agent, into cooperating with him. The SGC then learned that Senator Robert 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. (SG1: "Chain Reaction", "Smoke and Mirrors")
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 the Tok'ra symbiote poison to indiscriminately attack a number of Goa'uld-held worlds in 2004, an action that claimed the lives of several Jaffa armies and Tok'ra operatives before both the SGC and rebel Jaffa put a stop to it. (SG1: "Endgame")
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. While 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. (SG1: "Covenant")
Eventually, however, several agents of the Trust were taken over by the Goa'uld, who quickly infiltrated and took command of the entire organization after several Trust members used Osiris' Al'kesh to escape from Earth after a failed attempt to steal Earth's Stargate and use symbiote poison. These agents were presumably captured and implanted and brought back more Goa'ulds with them which they used to infest the organization. Under Goa'uld control, the Trust attempted to orchestrate a nuclear war between Russia and the United States of America, thus destroying the Tau'ri, so that the System Lords could take the Ancient outpost in Antarctica and presumably use it as a means of either forcing their enemies to submit to them or use it against Earth. This plan was foiled by Brigadier General Jack O'Neill, Lt. Colonel Samantha Carter and Russian Colonel Chekov, who exposed the Trust's connections and convinced Russian President Yuri Mikhailov to stand down his forces. They also destroyed the Trust's Al'kesh 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 along with the Trust's Goa'uld leaders. Former Vice President Robert Kinsey was likely on board and killed when the ship was destroyed as well. Presumably the identified Russian Goa'uld agents were arrested and extracted from their hosts by the Tok'ra afterwards. (SG1: "Endgame", "Full Alert")
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. (SG1: "Ex Deus Machina")
One plan that it attempted to execute was the destruction of Atlantis, presumably due to the fact that the Goa'uld did not want the Wraith invading their territory, simply because while the Goa'uld wanted to enslave the population, implanting them with some of their own symbiotes, essentially turning them into slaves, the Wraith would simply feed off the human population. 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' Zero Point Module 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 (ironically 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 Lt. Laura Cadman. The Goa'uld completely exposed himself and swore never to give up the needed code, but was tased by Lt. Colonel John Sheppard, allowing Caldwell to temporarily regain control of his body and give up the needed code which thwarted the Trust's plan to prevent the Wraith using the city to gain access to Earth and the Milky Way which would have likely been a threat to Ba'al's plans for rebuilding the Goa'uld Empire. Afterwards, the Goa'uld agent was extracted by Hermiod with Asgard beaming technology and presumably killed, depriving The Trust of an extremely valuable agent while Caldwell returned to himself and his relationship with those associated with the Atlantis Expedition including Sheppard and Dr. Elizabeth Weir greatly improved. (SGA: "Critical Mass")
Ba'al's final clone was finally apprehended and killed in 2008 by the Tok'ra after he killed all of his remaining clones himself. The real Ba'al was also killed when he traveled back in time to 1939 by an alternate Colonel Cameron Mitchell to prevent him from altering the timeline. Nothing is known of the Trust's fate since the death of its leader; however, it is very unlikely that it followed him to his grave. It is possible that Athena, the last remaining known Goa'uld on the planet, took over from where Ba'al left off as she was in the body of Charlotte Mayfield and seemed to be his second in command. Besides Athena it is unclear if there are any other Goa'uld Trust members left with the death of Ba'al and the fact that the Trust still has human agents. (SG1: "Memento Mori", "Dominion", "Continuum")