Aquaflash, born Arthur Allen, is the son of a human lighthouse keeper and an Atlantean queen. His unique heritage gives him the ability to survive underwater and control aquatic animals.
When Arthur was young, a time traveling speedster, Professor Manta, attempted to kidnap him and bring him to the future. His father prevented the kidnapping attempt, but the exertion of doing so caused him to die from a heart attack soon after.
Grief stricken over his father's passing, Arthur took to living in the sea. While cleaning up a chemical spill in the ocean, he was struck by a mysterious bolt of lightning. The electricity from the lightning infused the chemical pollution into his body, connecting him to the extra-dimensional speedforce. Now the fastest man alive, Arthur became capable of feats even more incredible than before.
Using the Cosmic Trident, the newly named Aquaflash travelled to the future to take his revenge on the man he perceived to be his father's killer. But he learned too late that he had not traveled far enough, and the man he killed was actually Professor Manta's father, the spitting image of his son. The young Professor Manta swore that he would one day learn the secret of Aquaflash's super speed, and travel to the past to take his own revenge.
Remorseful, Aquaflash vowed never to take a life again, and traveled back to the past to spend the rest of his life as a altruistic superhero. Now he protects the city of Central Bay from villains such as the Cold King, the Gorilla Scavenger, and even his own twin brother Cobalt Master.None of that is canon by the way. I just made it all up.