Hoskins was a member of the group called "The Trust" which was comprised of former rogue NID agents who believed that they had the right to use any means necessary in order to protect Earth from any and all threats including the Goa'uld.
When Krista James killed Doug McNair in self-defense, he, Jennings and Brooks framed Teal'c for the murder and kidnapped Krista. They then blackmailed Dr. Daniel Jackson into translating Ancient text for Osiris' Al'kesh that was left in Earth orbit. (SG1: "Chimera", "Affinity")
He and The Trust paid Dr. Hugh Bricksdale to use Osiris' Kara kesh to get to Osiris' Al'kesh. They used the Asgard transporter to steal the Stargate and used it to launch symbiote poison attacks on several Goa'uld worlds. When Stargate Command began investigating the disappearance of the Gate, they questioned Bricksdale and he set a meeting with Hoskins. They ambushed him and he was shot with a Zat'nik'tel by Lt. Colonel Samantha Carter, who used his locator beacon to beam up to the ship. He was saved by Brooks and beamed to the ship. When Dr. Daniel Jackson convinced Bricksdale to use the Kara kesh to beam him to the ship, he shot him with a Zat but after Jackson deactivated the cloak. When Teal'c dialed into the Gate, he was killed by Teal'c with a Staff weapon blast to the chest when attempting to kill Jackson and Carter. (SG1: "Endgame")