Admiral Augusto Nguyen is an Admiral in the United Nations Navy.
He's a squat and powerfully built Asian man from Earth.
After the events of the Ganymede incident Augusto attends a meeting with Chrisjen Avasarala, Admiral Souther, General Adiki-Sandoval, General Nettleford, and Mike Agee on whether they should accept a meeting with Martian Congressional Republic. Chrisjen tells them to find a way to make it work as she leaves with her personal assistant Soren Cottwald. Later he is put in charge of the security arrangements for the Martian delegation to discuss the incident.
When the King was overrun by the protomolecule and Jim Holden boarded it to retrieve the bioweapon launch vehicle remote codes that would stop the protomolecule hybrids from reaching Mars, Nguyen withheld the codes in exchange for being rescued off the ship. As a response, Holden shot him in the throat, killing him.