Todd Arliss was an Olympic champion swimmer until he was seriously injured saving a man who had fallen overboard during a sea cruise. Arlis hired criminal scientist Dr. Lemuel Dorcas to restore his health and willingly took part in an experiment to fuse his genetics with those of a captured Namor and a shark. Renouncing his humanity, Arlis took the name Tiger Shark and has clashed with Namor several times, even managing to take control of Atlantis on more than one occasion.
Arliss can survive in air or water, but weakens rapidly away from water. At his peak, Arliss has tremendous superhuman strength, stamina and durability, as well as enhanced speed (superhuman while swimming), agility and reflexes. His costume is lined with an internal water circulation system which keeps him constantly moist. His mutated physiology has fluctuated over the years, alternately enhancing or impairing his powers and mental facilities.