Mr. Green was a medic for the Resistance and later drug dealer in the aftermath of the Combine's downfall.
Mr. Green worked with the Resistance as a medic and operated at different Vortigaunt camps out in the coast. On an occasion he spotted Gordon Freeman passing through the camp.
Following the Combine's downfall Mr. Green moved into the countryside and bought a farm which was located near a stables and family park. He began to grow drugs and distribute them for profits. This career choice came to be as he didn't properly qualify as a medic, therefore had no more employment after the Combine were defeated.
Nathan Johnson and Hannah Robertson stumbled across the farm. With two witnesses coming across his operation Mr. Green displayed a more ruthless side and he snatched Hannah, taking her to a river to drown her. Nathan arrived on time and shot Mr. Green, who toppled into the river and presumably drowned.
But he survived his fall, and wanting revenge tracked Nathan down to his apartment in City 17. Mr. Green broke in, only to find Nathan's friend Sarah Woods alone there. He tied her up to a chair and plotted to set up a small explosive device, which would detonate once Nathan returned home, thus killing both him and Sarah. But Nathan arrived early and stumbled upon Mr. Green. Before Mr. Green could draw out his gun, Nathan shot him dead.
Nathan swore Sarah to secrecy and said he would deal with Mr. Green's corpse. The whereabouts of where Nathan took Green's body is unknown.
- Mr. Green uses the Arne Magnussen model from Half-Life 2: Episode Two, but modified to wear a green suit.
- His location and near encounter with Gordon Freeman during the Half-Life 2 campaign is at the Vortigaunt Camp during the "Sandtraps" chapter.