Simon Wallis is a medical doctor and Elizabeth Weir's fianceé, whom she left when she took command of the Atlantis Expedition. He is portrayed by Garwin Sanford, who also portrayed the Tollan named Narim in several episodes of Stargate_SG-1.
In a recorded message sent from Atlantis, Dr. Weir told Simon to "move on", fearing that she might never return to Earth. When she did briefly return, however, she found that he had followed her advice and found someone else. (SGA: "Rising", "Letters from Pegasus", "The Intruder").