Changeling

Erik Razar first gained his powers during an attempt to escape from prison, where he was electrocuted attempting to turn off the prison’s power supply. Shortly after this he learned he now possessed the ability to become any animal he chose, before taking the moniker of Changeling. 
 
Now out of prison Changeling soon runs afoul of Jay Garrick, the original Flash. The two soon meet in battle, which takes place beneath the sea, as Changeling adopted the form of a shark as The Flash began to drown, in desperation he smashed his foes head on a rock, killing him in self defense. Following Razar’s death Flash gives the body to scientist in order to discover what facilitated the change in him.