The Wraith Keeper was the leader of a group of Wraith who guarded their Hive ship while the rest hibernated. When the Wraith culled some of the Athosians, they also captured members of the Atlantis expedition. She had Colonel Marshall Sumner brought to her, and learned of Earth, with its large population. Eager at the prospect of a new feeding ground, she demanded to know where Earth was, but Sumner refused to tell her the Stargate address, so she fed upon him. Major John Sheppard attempted to stop her, but he was forced to kill Sumner instead. When Sheppard was brought before her, she recognized the Lantean Life signs detector he was carrying. Lt. Aiden Ford was able to interrupt the Keeper's attempt to feed on Sheppard by killing the Wraith warriors guarding her, and Sheppard then killed the Keeper by driving the blade of a Wraith stunner rifle into her chest.
While the Wraith Keeper's death allowed the team to escape with the rest of the Athosians, it also caused the rest of the Wraith to emerge from their hibernation cycle fifty years prematurely with the knowledge that there was a rich new feeding ground available, and that the only way to get to it was through Atlantis. (SGA: "Rising, Part 2")
After tapping into her abilities, Teyla Emmagan learns that the Wraith are coming to Atlantis in order to reach Earth. Sheppard realizes that the Wraith learned about Earth through the Wraith Keeper's interrogation of Colonel Sumner. (SGA: "The Gift")