Ensign Masaro was a Human Starfleet officer serving aboard the Enterprise NX-01 in the 2150s.
Masaro was on Enterprise during its mission in the Delphic Expanse to stop the Xindi superweapon. He was discharged by Phlox from Sickbay following the Battle of Azati Prime. (ENT: "Damage")
Unknown to anyone at the time, Masaro was also a member of the xenophobic extremist group Terra Prime. In this capacity, Masaro supplied to John Frederick Paxton, Terra Prime's leader, genetic material of Commanders Tucker and T'Pol in 2155, for the purpose of creating a binary clone, with which to further their agenda of human superiority.
When Captain Archer decided to lead a small team to infiltrate Paxton's base on Mars, Masaro covertly sabotaged the team's shuttlepod, nearly causing them to crash. Later, when it was discovered that Masaro was the saboteur, he confronted Captain Archer with a phase pistol. Apologizing to Archer for his actions, Masaro put the phase pistol to his own head and committed suicide. (ENT: "Terra Prime")