Simon was a gifted but deeply troubled boy due to his loss. He only communicated through telepathy and people that he liked, such as Elizabeth Lochley, whom he greeted with an image of a bouquet of flowers.
Simon was a tunnel rat living in the ducts and pipelines beneath Mars Dome One. While living there, he was involved with a young girl who died under mysterious circumstances. He blamed himself for her death and hoped to make-up for it someday, vowing never to speak again until he did so.
In about 2261, he met and became a part of Byron's group of telepaths and adopted their ways and beliefs. In 2262, he followed Byron and rest of his followers to Babylon 5. While being examined by Dr. Stephen Franklin, he sensed something and entered the ventilation ducts to investigate. Hearing the chiming sounds coming from John Clemens's porcelain ballerina, he picked up on what he was thinking about thus learning about the assassination plot. Stunned by what he saw he made a noise and was heard. Clemens shot up at the vents and hit him. Shot and losing a lot of blood, Simon dragged himself to the conference room were John Sheridan was. Limping in, he collapsed and sensed that the killer was there and said "No" out loud and beamed the thoughts of the assassin into everyone’s minds, thus helping to save Sheridan’s life. Then he died. It was this sacrifice that convinced Sheridan to allow Byron and his followers to settle on the station.