Commander Devlin was a commander in the United States Armed Forces.
Background
He was the leader of the military personnel at The Divide.
Judging from the entries found on a terminal in the Third Street Municipal Building he's a very patriotic man, reluctantly instructing his men not to engage the peace protesters. In a second entry he mentions an upcoming visit of General Wellesly.
Appearances
Commander Devlin is only mentioned in the Fallout: New Vegas add-on Lonesome Road.