Jeff Walker was an astronaut on the Mars mission. He was abandoned on the planet surface after caught in a dust storm and unable to reach the landing craft before it returned to the ship. Maddux Donner piloted the lander and was ordered to leave both Walker and Sharon Lewis on the planet by Mission Commander, Mike Goss. ("Pilot")
During the mission, Walker had a series of health related problems and while on Mars, he began struggling to breathe.
10 years later, during the Antares mission it was finally revealed to Donner and Shaw that the true mission on Mars was to retrieve the Alpha object and that the major contributing factor to the mission's failure was that Jeff Walker was not chosen by Beta. He was not supposed to be part of the mission. The events of the mission are the reason Eve Shaw has had such control over selection of the Antares crew. ("Déjà Vu")