|Out of universe information|
One day, his daughter Sharon Wallace was diagnosed with leukemia and was told to say his goodbyes. Wallace didn't want to do that, since he already lost his wife. However, he later noticed that Stargate Command had several advanced technologies including nanites and stole some to save his daughter, knowing this would get him arrested. However, the nanites weren't working, so he arranged to have Jeannie Miller and Dr. Rodney McKay kidnapped, to help save his daughter by reprogramming them. When they tried to escape, Wallace injected the nanites to Jeannie in order to make them work. After his daughter was saved, the nanites stopped her heart and repaired her heart condition. When trying to find out a way to shut down the nanites, Wallace was suddenly arrested by Lt. Colonel John Sheppard and his team.
McKay gets Todd to help shut down the nanites, but learns that Sharon had died because the nanites "ran out of steam" and no longer functioned. When trying to shut down the nanites to stop them from repairing Jeannie's epilepsy and shut down her brain, which would kill her, Todd needed to feed. Sheppard went to visit Wallace and told him the situation. After he lost his daughter, he was guilt-ridden by the fact that he would be responsible for another death, he sacrificed himself in order for Todd to complete the shutdown program. (ATL: "Miller's Crossing")