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|Out of universe information|
Simeon was a seasoned criminal before finally begin recruited by the Lucian Alliance, coming from the same clan as Ginn. He served the Lucian Alliance on the Icarus-like planet as part of the team that was to travel to Destiny to claim it for the Alliance. (SGU: "Malice") 
After Kiva was shot, Simeon questioned the wounded Col. Telford as to how both of them had been shot, not believing Telford's description of events. Simeon was later escorted to a holding area on the ship after the ship was taken back by the expedition. He was later interviewed by Camile Wray to determine if he had any information that could prove useful, being selected to remain on the ship. (SGU: "Intervention", "Aftermath")
He was very displeased at Col. Young's intention to keep them all locked up forever. He later went for a medical check-up and wanted to see TJ's ability to protect herself which she aptly demonstrated. Despite being allowed to roam the ship under guard, he continued to have conflicts with the crew - most notably MSgt. Greer who continually tried to provoke him so he could have him locked up. He also mentioned an inappropriate comment to Dr. Park and then was sent back to his quarters.
He revealed to Varro that he had been supplying the expedition with misinformation and was shocked that the others were supplying correct information. Varro mentioned that Simeon was from a rough planet compared to many of the other Lucian Alliance members that explains his behvior. (SGU: "Awakening", "Pathogen")
EscapeSimeon managed to overpower and kill Michaels, the soldier guarding him, and escaped unescorted onto the ship. He went to Ginn's quarters and found her there. She too was unescorted due to the fact that her body was being used by Dr. Amanda Perry. He killed Ginn, and by extension Dr. Perry and left. He shot two more guards outside the armory and gathered some supplies such as Lucian Alliance Bombs and weapons, made his way to the gateroom where he took Dr. Park as hostage and had Dr. Volker dial a planet for him.
He escaped through the Stargate with Dr. Park, planted an explosive device on her back and retreated. He made his way across the planet hoping to get far enough away so those on board would not have time to retrieve him before Destiny jumped back into FTL. He set a trap for those that followed planting explosives in the ground to kill those who came after him. He managed to evade the soldiers but Dr. Rush did not give up, he used some C-4 to scare some creatures into stampeding. The creatures trampled Simeon, injuring him. He told Rush that he had information, most likely about the planned attack on Earth, but Rush shot him anyway. (SGU: "The Greater Good", "Malice")
Simeon is very strong and intimidating but in a more crafty and wiry way as opposed to big and muscular. He is imposing and scary in a very unpredictable way. He holds many secrets and is willing to die or kill others in order to protect those secrets.