The Bio Suit was an experimental exo-skeleton developed by Dr. Hugo Schneider, Alvin Severnya and Marvin Simmons in the early 2000s. It was supposed to be a combat unit capable of enhanced speed, strength and regenerative capabilities.
Due to conflicting moral principles, Severnya and Schneider kept the suit's real purpose a secret from Marvin Simmons and instead told him the suit was only supposed to cure illness and cancer. Since he was the engineer, he had no knowledge of the biochemical functions of the suit.
Simmons, however, found out about the deception and decided to steal the suit and the blueprints. It is currently unknown what happened but the suit ended up in the hands of Simmons' son Thomas Simmons who tried continuing his father's work under the impression it was supposed to cure cancer.
During the Incident, the still incomplete suit and Thomas fused, creating the superhero known as Nightfighter. The suit saved Thomas' life when everything around him exploded and afterwards, for a short time, changed his physical appearance according to his innermost needs. This ability vanished quickly, however as Simmons is now stuck inside the suit, unable to even remove the helmet.