The Monitor is a Special Operative of the Dominion, who is both Lancer and Cypher at the same time. He appears to use a variant of the Storm javelin as shown by is ability to use Wind Wall when blocking attacks in cutscenes and a electric attack to kill Tasyne’s operative inside the Regulators.
He was at Freemark when it was destroyed by the Cenotaph and was one of if not the only surivor. In this event he Heard the anthem. This lead him on a mad persuit of its power. Throughout the game his aim is to get back to the Heart Of Rage (Freemark now as a Cataclysm). He eventually achieves this goal and merges with the anthem becoming the games final boss.