Mann was Professor Brand's protege and leader of the Lazarus missions. He convinced eleven scientists to join him on a one-way mission to survey twelve potentially habitable worlds on the other side of the wormhole. He was considered "remarkable" and "the best of us" by his colleagues.
While on Mann, he and KIPP explored the icy surface only to discover that it was inhospitable for human life. They decided to use probes to drill deep into the ice clouds in the hopes of finding the planet's rocky surface.It is clear in the short comic Absolute Zero that Mann realized that his planet would not be best suited to receive humanity after observing the results from his probes, which revealed that his planet has no real surface as the planet had seemingly endless layers of ice cloud. Desperate for rescue, Mann had KIPP produce a hypothetical data set for a good life-sustaining planet before decommissioning him and using his power cell to provide power for his hypersleep chamber.
Mann is reawakened by the crew of the Endurance approximately 30 years later due to the time dilation on Miller. Mann's hypersleep chamber was critically low on power at this point and Cooper had to manually break open his sleep-bag to wake him. Dr. Mann is visibly shaken by the appearance of people coming to his rescue, stating he had not set a waking date. It is then revealed that he and Professor Brand knew that Plan A was impossible and that the only contingency that allowed for human continuity was Plan B.
Once the truth about Professor Brand's Plan A was revealed, it was decided that Cooper would return home while Mann, Romilly and Brand would proceed to carry out Plan B on Mann's planet. Dr. Mann, secretly knowing his planet could never support human life, then attempts to murder Cooper, seeing his death as necessary to complete the mission - Plan B.Mann did not want Cooper to return to Earth with the Endurance, as he now needed it to reach Edmunds' planet with the remaining crew to start a colony. He planned to lie about Cooper's death being an accident and later on, tactfully introduce the idea of colonizing Edmund's planet instead, since conditions were more favorable for human life, and the Endurance was available for the journey.
After witnessing the explosion in his landing pod, signaling the death of Romilly and hearing that Cooper survived his attack with Brand on her way to help, Mann adjusted his plan and instead decided to maroon the crew of the Endurance on the planet in order to initiate Plan B. He only succeeds in stealing Ranger 1, docking it imperfectly on the Endurance. He is killed instantly when the airlock depressurizes despite Brand and Cooper's warning.