Planet in the Pegasus Galaxy. During a mission to this planet John Sheppard encountered an alien lifeform which entered him and was brought back to Atlantis. It traveled from person to person by physical contact and caused horrifying nightmares, then seemed to feed off the victim's fear.
HOME TO - Uninhabited
FIRST APPEARED - Doppelganger
Doppelganger - While investigating a seemingly uninhabited world the team come across a glowing crystal.