A computer security expert, he worked for an international consulting firm. He found himself in trouble after breaking into CIA servers to investigate his brother's death, a soldier who died in Afghanistan. It brought him into conflict with Terence Beale and his team, but was saved by the intervention of Reese, who also convinced him that his brother was a hero who died in the service of his country.
Alex Duncan's older brother, he was a Pentagon intelligence officer who went undercover in Afghanistan as a military advisor by the name of Brent Tomlinson. He sold information to the Taliban and was subsequently investigated by Reese and Kara Stanton on orders from their superiors. Reese killed him after he failed to convince him of his innocence.