Steven Caldwell's Goa'uld

A Goa'uld working for the Trust managed to take Colonel Steven Caldwell as a host. He soon rigged the ZPM used to power Atlantis to explode by removing the failsafes to retained power, in the hopes of preventing the Wraith from making it to the Milky Way. He also sent a distress call to the Wraith, and caused the city's inertial dampeners to power up. Laura Cadman soon discovered that Caldwell's access code was used to access the Atlantis' operations. The Goa'uld warned John Sheppard and Ronon Dex that would easily defeat them, but Ronon was able to easily overpower him, and Sheppard tasered him, allowing Caldwell to resurface and tell them the required access code. Hermiod then used beaming technology to remove the symbiote from Caldwell. Caldwell survived, but the symbiote's fate is unknown.