A Starfleet ensign aboard Enterprise who secretly works for the xenophobic movement Terra Prime, sabotaging the ship's efforts against John Frederick Paxton before confessing and taking his own life.
Ensign Masaro is a member of Enterprise's crew in the two-part story Demons and Terra Prime, set in January 2155. Outwardly loyal, he has been recruited by Terra Prime, the movement demanding that all aliens leave the Sol system.
Masaro is the source of the security breaches that puzzle Jonathan Archer, including the theft from the ship of the genetic material Paxton's scientists used to create a child of Trip Tucker and T'Pol. Suspicion falls first on others, among them the reporter Gannet Brooks and the engineer Kelby.
Confronted by Archer, Masaro admits what he has done and says he believed he was protecting humanity. Overcome by shame, he shoots himself with a phase pistol before he can be taken into custody.