The Trolls are a villain group in the now-defunct City of Heroes MMO.
"Trolls" are people mutated by the illegal substance Superadine. In moderate amounts, the substance gives people superhuman abilities, usually in the form of strength and limited invulnerability. However, if you take too much of the substance, you begin to physically mutate.
The Transformation Process
The first stage is a drop in intelligence. You begin to exhibit aggressive behavior, almost animalistic in nature. Your skin starts to take on a greenish hue and your eyes begin to change color to green.
The next stage is more profound. Your skin changes color to green. You develop canine incisors. Your ears begin to develop points, and small stubs begin to form on the frontal part of the forehead. You still retain some level of intelligence, and while you are strong and more durable, you still rely on physical weapons such as firearms.
The third stage is where the real "troll" begins. Physical mass increases. The skin is now a bright shade of green and you begin to glow. Hair loss is now complete, and fully-developed horns have formed on the forehead. Those canine incisors have grown into fangs.
The "final" stage is often called the "supa-troll" phase, where the subject has increased in mass and size. They are now hulking monstrosities. In addition to the complete hair loss and the growth of horns and fangs, the already-bright green skin is now completely glowing in bioluminescence. What little intelligence they exhibit at this point is reserved for eating and fighting, and they are easily provoked.
(Check out their Paragon Wiki entry for more information.)
The Trolls were the featured villains in the comic series Troll Kid.