the main protagonists are j. robert oppenheimer -lrb- strathairn -rrb- , the brilliant physicist from berkeley , and major gen. leslie r. groves -lrb- dennehy -rrb- , the blunt , forceful , overbearing head of the manhattan project who hires `` oppie `` to direct the los alamos bomb laboratory because he 's virtually the only scientist he trusts and can communicate with .