ZX (Dennis Thornton) is the third agent to be introduced on this wiki. He was the 4th G. I. Unit: 5 member hired.
When a baby, he, his mother and father, Govenor Samuel Thornton, were flying to the Caribbean for their yearly vacation on their private jet. On the way, their jet was shot down by a helicopter being flown by Ronald Ramsey III, and his teenage son, Ronald Ramsey IV "Ron", a deadly assassin and a deadly assassin in training. The plane crashed on a massive island in the Pacific. All three of the passengers survived, but not the pilot. The helicopter landed and out stepped Ramsey III and Ramsey IV. Fortunately, G. I. Unit: 5 had been following the helicopter and surrounded it with fighter jets. Ramsey III and Ron ran into the woods and took the Thorntons hostage. Ron was found and captured but lied and said that his father had died when they "crashed" in the helicopter. He also said that the Thorntons were dead, so Ron was taken to prison. Meanwhile, after the first month on the island, the govenor and his wife, Patty died of the wounds caused by crashing on the plane. Ramsey raised ZX saying that he was his son, and taught him how to walk, talk and hunt. Every year a cruise ship would go by and Ramsey would try to signal it with a mirror of the helicopter. One day, Ramsey died and revealed to ZX that he was not his father. Now ZX would try? to survive on his own and try to spot the cruise ship. All attempts to summon the ship failed until one year. When ZX (called Dennis) was 20 years of age and was hunting baby shark near the island. As he speared a shark with a spear he made out of sticks, vines, and rocks, all of the sudden a Great White came and saw him. Most sharks would leave and look for a seal but it moved toward Dennis. Dennis held his breath and tried to swim away from the beast, but it kept following. It was moving to fast for him to jump onto shore so Dennis grabbed some sand and through it into the eye of the shark. The shark turned around as Dennis took a out a knife given to him by Ramsey. He jabbed the shark in the back but instead of stabbing, the knife slipped off the shark skin. The shark turned around and went after Dennis again. Dennis pushed his face out of the water to get a breath and saw that he had moved far away from the water. He saw the shark coming at him with his jaws opened. Dennis through his spear into the mouth of the shark. Finally, the shark fell to the ground. Dennis took one of it's teeth for a souvenir. When he pushed his head out of the water again he saw the cruise ship not more than a kilometer away. The ship spotted him to and pulled him aboard. After he reached shore he asked the police who his real father is and found out that it was Ramsey and his son's fault that they died. One year later, Lief Jackman offered him a job on G. I. Unit: 5, hearing the brace warrior he was surviving on that island. ZX accepted thinking he would finally get revenge on Ramsey IV, but that was talked out of revenge by X.
ZX is 6' 2" and 32 (according to G. I. Unit: 5 01). He has blonde, short, crazy hair.