M. Romero was a Human male who served as a Military Assault Command Operations soldier during the 22nd century. In the year 2153, Romero was assigned to the NX-class starship, Enterprise for it's Delphic Expanse mission.
Romero ate lunch with fellow MACOs Major Hayes, Corporal Chang, and Sergeant Kemper in the mess hall in 2153, upon their first meeting Ensign Hoshi Sato, Enterprise's communications officer. Shortly thereafter, he participated in the rescue mission to retrieve Captain Archer, Commander Tucker, and the Xindi Kessick from a trellium-mining facility. (ENT: "The Xindi")
M. Romero was played by Marco Sanchez.
In the final draft script of "The Xindi", Romero (and three MACO men with him) was described as "accustomed to a more formal, chivalrous atmosphere" than that aboard Enterprise, prior to joining the ship.
Due to re-use of costumes and name tags, Yuri Elvin and Mickey Cassidy were also among the performers who portrayed a "M. Romero", but with different ranks.