Deadmen

Deadmen (デッドマン, Deddoman) are people who are infected with the Nameless Worm which enables them to do extraordinary things with their blood. Most of them were infected during the Great Tokyo Earthquake.

Ganta Igarashi is an exception for he was infected much later by a unique Nameless Worm by the Wretched Egg herself, during the Nagano school massacre. He became a Deadman with a unique ability, that is the key to the Mother Goose System.

During the Great Tokyo Earthquake, pieces of a certain Red Diamond were found. People ended up ingesting pieces of this "Red Diamond". The Diamond is a capsule for the Nameless Worm parasites and so, said parasites settled inside the bodies of their victims and gave them their unusual abilities. These parasites were somehow released by the Wretched Egg during the Great Tokyo Earthquake.

Capture
The privately owned prison, Deadman Wonderland, is a facility where Deadmen are held (more specifically in G Ward). They are used to compete against each other in the Carnival Corpse. Tsunenaga Tamaki researched the Nameless Worm and was able to create artificial Deadman: the Forgeries from data he thought he obtained from Hagire Rinichirō's computer. The Forgeries' powers are based on a supposed Anti-Wretched Egg poison. This, however, turned out to false as the real data was hidden.

After Makina overthrew Takami and shut down Deadman Wonderland, all the Deadmen had a re-trial. Those who committed actual crimes were transferred to a normal prison (like Minatsuki Takami and Chaplin Sukegawa) and those who were innocent were released (such as Senji Kiyomasa and Ganta Igarashi), though, it was difficult for many to adjust to a normal life after being in the prison for so long.