Dr. Simon Wallis is a medical doctor and Elizabeth Weir's fianceé, whom she left when she took command of the Atlantis expedition.
In a recorded message sent from Atlantis, Dr. Weir told Simon to "move on", fearing that she might never return to Earth. When she briefly returned, however, hoping to convince Simon to join the Atlantis expedition, she found that he had followed her advice and found someone else. (SGA: "Rising", "Letters from Pegasus", "The Intruder")