The US military made a horrible mistake when trying to converge the FEV virus with a death claw embryo to make a secret tool of destruction that was going to be unleashed on Bejing before the bombings, but under drastic conditions things went wrong and years after the bombings the monster is growing and is ready to rise from the ruble of the lab under the Capitol Building.
Gyrronement was an experiment that was thought to be the answer to the nuclear threat of China, but before completion one of the scientist noted that the cell structure of Gyrronement's embryo was growing rapidly so they decided to give up on this experiment before their creation grew out of control, so to terminate the embryo they shot gamma rays into it to destroy it but the gamma rays were absorbed into the embryo and it didn't stop the growth it made it stronger. But unaware of this the scientist were about to clean petri dish when the alarms sounded and they left to take cover thinking that it wouldn't matter if the petri dish was sanitized since they were about to be nuked, but they were wrong.
After The BombingsEdit
After the bombings the scientists died and the radiation made Gyrronement more powerful and after 200 years the creature has completed growth and is currently roaming the metro system feasting on ghouls, feral ghouls, raiders, super mutants, and the occasional Brotherhood of Steel member.
Though he has been spotted many times, he has never been confronted by anything that had any intentions of killing him, not that anyone could kill him and he currently lives in Capitol Building when he isn't roaming.