Edwin C. Steen, codename Lifeline, is a medic and scientist for G.I. Joe. He is incredibly pedantic.
Lifeline was among the G.I. Joe doctors operating on Snake Eyes following his injuries in the town of Springfield. During the operation, Snake Eyes suddenly regained consciousness and grabbed Lifeline by the throat, the ninja still thinking he was engaged in combat.
Years later, following the shutdown and reformation of the Joe team as an international organization, Lifeline remained a member of the team. When the head of Decepticon Astrotrain crashed on Earth, Lifeline was part of the Joe unit sent to study and retrieve it. Studying the head to ensure it wasn't dangerous, Lifeline detected a strange energy signature that was keeping the head alive, as well as causing the surrounding plants to grow rapidly. The Joes were then ambushed by V.E.N.O.M., who were there to steal the head. Lifeline tried to escape in a V.A.M.P., only to be forced off a cliff by Sly Rax. Lifeline awoke in M.A.S.K. HQ where, much to his displeasure, he was being treated by Julio Lopez. Lifeline told M.A.S.K. and the Joes that the energy he detected came from a techno-organism that could be used either for medical miracles or untold destruction. After Julio was injured in battle with Sly Rax, Lifeline told Matt Trakker that the only way to save his life would be through the use of the techno-organism from Astrotrain's head. Matt and Scarlett recovered it from the hands of Miles Mayhem, and Lifeline was able to complete a surgery that saved Julio's life.
Though he had some trouble understanding his alien physiology, Lifeline was still able to stabilize Doc Senior after he took some shrapnel protecting Grand Slam, revealing himself as a Dire Wraith in the process. He later spoke up to ask about the whereabouts of Doc's daughter. When Doc Jr. returned to the field and was locked up in her room, Scarlett informed him he was now G.I. Joe's chief medical officer. With his new authority, Lifeline immediately said that Doc Jr. should be locked up in the lab for study since she was a Dire Wraith, something Grand Slam took great offense at given that her father had saved his life.
Given that he happened to be among the first Joes he saw, Shipwreck hastily chose Lifeline to be part of his team responding to V.E.N.O.M. agents Ice Queen and Stiletto raiding museums in St. Petersburg, riding shotgun in the Crossfire with Cover Girl and Salvo.
- The "C" does not stand for "Charlemagne". Apparently.