Grand Zealot Brian Richter was a lieutenant in the Enclave. On a scouting mission, he and his team went to capture a reserve of fusion cores from a pre-war disposal facility. The team engineer however, failed to set the door locks correctly, trapping them all inside. He was the only survivor due to his then unknown immunity to radiation. He was then rescued by High Confessor Tektus and nursed back to health by the Archemist.
Convinced that this immunity was a gift from Atom, and the reason he survived, Richter decided to join the Church of Atom.