They are descended from a group of people in the 20th century who could not cope with the pressure of modern technology so they retreated underground and their bodies mutated and warped to adapt to the environment underground.
They started mass-abduction of people in Mega-City One and after the most recent abductions, Dredd follows them by using the infra-red headlamp to follow the heat of their footsteps. When Dredd arrived underground, he was captured by a swarm of Troggies.
After Dredd was captured, he finds out that the people who was abducted are being used as slaves in a labour camp and Dredd was introduced to Slick Willy, leader of the Troggies. Dredd learns who they are and tells them to surrender quietly and the Judges will go easy on them, Slick refuses and reveals his plan to plant explosives at certain points in Mega-City One and then blow up the city in retaliation for driving them underground. Dredd states that the Troggies will be killed as well and Slick states that they haven't got anything to live for and then made Dredd join the other kidnapped people.
After Slick Willy announced that the Troggies are going to the Grand Central for a celebration, he states that in 60 "Big Ones", the detonator will be pressed and Mega-City One will be destroyed. After leaving, their two Troggies guarding the prisoners and Dredd antagonises another prisoner so he can let the prisoner throw him towards the laser drills, which he uses to kill the guards. He then grabs his communicator from one of the guards and tells Judge Control to switch on the power in the subway station and to send a clean-up squad to the Grand Central.
Dredd proceeds to use an underground train to go to the Grand Central and after he was noticed by the Troggies, he uses the lights in the subway to blind them due to them being adjusted to the dark. Slick Willy then attempts to activate the detonator but was stunned by Dredd and he manages to catch the detonator, saving Mega-City One from destruction. The Troggies were then arrested and ends with Dredd saying the city is full of people like the Troggies and no Judge can rest until their all gone.