Gergerra Rei was a Mech-Lord, possessing a high status as the master of the Kapekan Sect of the Mechanicum's Legio Cybernetica branch. During the Great Crusade in the late 30th Millennium, he led two full cohorts of combat automata (Imperial Robots) which fought alongside the Luna Wolves Space Marine Legion and the Warmaster Horus during many notable campaigns. Like many members of the Cybernetica, Rei eschewed the gross cybernetic augmentations of his colleagues in the Mechanicum in favour of subtle enhancements that did not disfigure or dilute his outwardly human aspect. However, those who knew Rei knew that whatever humanity he did show was rare and fleeting.