Mortimer Norris was originally a petty criminal who worked for the Maggia, a crime syndicate that often clashed with superheroes. One day, he was assigned to steal some radioactive isotopes from a truck, but he accidentally exposed himself to the radiation and fell into the East River. He became a fish-like creature with green scales, fins, gills, and superhuman strength when he resurfaced. He decided to use his new abilities to become a crime lord and called himself Mr. Fish. He also recruited a dwarf named Shrike as his second-in-command.

Mr. Fish’s first and only encounter with Luke Cage, Power Man, was in issue #29 of his solo series in 1975. Mr. Fish tried establishing his Maggia branch in Harlem, but Cage was hired to protect one of his targets. The two fought at a construction site, where Mr. Fish used a concussive ray gun to knock out Cage. However, Cage recovered and defeated Mr. Fish’s henchmen. Mr. Fish then charged at Cage with a steel girder, but Cage dodged, and Mr. Fish fell off the building, apparently dying on impact.

Mr. Fish was not seen again for decades until he was revealed alive during the All-New, All-Different Marvel relaunch in 2016. He appeared in Power Man and Iron Fist (Vol. 3) #10, where he warned Tombstone, another crime boss, that Black Cat was planning to take over his territory in Harlem. He later appeared in Runaways (Vol. 5) #7, where he was attacked by Alex Wilder, a former Runaway who had become a sorcerer and a criminal mastermind. Wilder used his magic to banish Mr. Fish to Hell.

Mr. Fish has also appeared in other media besides comics. He was featured in the video game Lego Marvel Super Heroes 2 as part of the Flashmob team that fought against Luke Cage and Iron Fist in Harlem. He also appeared in the animated series Ultimate Spider-Man vs. The Sinister Six as one of the villains who attended the auction for the Siege Perilous fragments.

Mr. Fish has a brother named Bill Norris, who became a fish-like mutant after exposure to the same radioactive isotopes as Mortimer. Bill took up the mantle of Mr. Fish and joined the Flashmob, a group of former Power Man and Iron Fist villains who sought revenge against them. He first appeared in Daughters of the Dragon #4 in 2006 and later joined the Hood’s gang of supervillains.