Scientist who traveled to the Pegasus Galaxy with the members of the original Atlantis expedition. He and Dr. Abrams accompanied Dr. Rodney McKay and Major John Sheppard to investigate an Ancient weapons platform that had been discovered on Atlantis's sensors.
Sheppard, however, was more interested in the Wraith distress signal his Puddle Jumper was detecting from a nearby planet. After consultation with Dr. Elizabeth Weir the Jumper was rerouted to the surface. While investigating the inside of a crashed Wraith cruiser Gall and Abrams discovered a Wraith commander that had awoken from hibernation. It pushed Gall aside and attacked Abrams, feeding off his life energy until he was a dead husk.
Gall was wrapped in webbing and taken to be fed upon later. After moving to a different part of the ship the Wraith fed upon him until he gave up information about their Puddle Jumper. It deliberately left enough life inside him to keep Dr. McKay occupied while Sheppard, now down to one man, went off to try and fight the Wraith. Gall, who had known McKay before this particular field expedition, found Rodney's opinion about self preservation had changed. He wanted to get into the fight to help the Major.
Realizing that's exactly what the Wraith didn't want to happen, and that Rodney's field training was not going to save him, Gall used the remainder of his depleting energy to take his own pistol and shoot himself in the head.
BEHIND THE SCENES
Writer Martin Gero often named characters after close friends. So it was with Brendan Gall. Gero traveled to Toronto to watch a play directed by Gall, and starring Kate Hewlett, real-life sister to David Hewlett. He was so impressed with her "Hewlett-isms" that he created an episode to feature her as Jeannie ("McKay and Mrs. Miller"). Jeannie had already been established as a sister of McKay. The party could not be complete without the real Brendan Gall himself, who played Jeannie's husband, Kaleb.
The Defiant One - McKay is instructed to keep watch over Gall in the event that the Wraith commander returns to finish his work, but Gall kills himself so that McKay can rejoin the fight.