Positron is the Iron Man/Captain Atom of the Freedom Phalanx, and the alter-ego of dev Matthew Miller.
Before becoming a superhero, Dr. Raymond Keyes was a professor of nuclear physics at Stanford. After his budget was cut and his access to the university's linear accelerator became limited, he took a corporate job in an effort to work for the greater good. However, he soon find out that not all companies shared his ideal. In an unfortunate (or perhaps fortunate) "industrial accident," Dr. Keyes found himself able to generate and control anti-matter. With his extended knowledge of nuclear physics, Dr. Keyes understood very well the capabilities of his power, and their danger.
In order to better control and focus his powers, he constructed a crude suit able to contain the anti-matter. This allowed him to fire anti-matter in the form of blasts, as well as a limited form of flying. He put his powers to the test when a group of Devouring Earth monsters attacked an amusement park and killed dozens of citizens. In the name of justice, Dr. Keyes tracked them down to their base and destroyed them. As a result, Devouring Earth has become his most hated enemies, and the feeling is mutual. When the media had asked him what his "hero name" was, he told them "Positron". Thus a hero was born.
The important thing to remember about Positron, however, is his high level of instability. While he once had control over his powers, after being injured in the Rikti War he became trapped in his suit. A large enough leak could mean bad news for all of Paragon (similarly to how the Siren's Call zone was destroyed by an out-of-control hero).
Positron stands guard in the center of Steel Canyon and gives out a Task Force to heroes leveled 10-15. This Task Force features the Clockwork, Circle of Thorns and Vahzilok, and is widely regarded as one of the worst in the game due to the long length, repetitive tasks and lack of a big finale fight.