Centuries ago, an ancient water-dwelling race built a hidden city beneath a mountain in the sea. Though these creatures had their enemies, the city was an impenetrable fortress, and, in the safety it provided, they grew complacent. Fizz, however, harbored a curious spirit that could not be satisfied living so cushioned a life. Unable to resist the allure of danger, Fizz had a habit of sneaking out of the city to look for trouble. In his many adventures he grew to be a powerful fighter with a keen resourcefulness that let him skirt danger with clever ease. One day, Fizz returned to find the city abandoned: his people had vanished, leaving Fizz without a clue to explain their disappearance. With nothing left in the city to keep him, Fizz salvaged an enchanted trident from the ruins and set out alone.
For years, Fizz wandered the ocean, using the skills he'd learned during his adventures as a young boy to survive. Finally, Fizz discovered the port of Bilgewater. He was fascinated with the existence of life above the water and could not resist exploring the island. In his endless curiosity, Fizz inadverently meddled in the affairs of the humans who lived there and his presence did not go unnoticed. His mischief angered many residents who eventually sought to capture or kill him. Fizz found himself cornered, and he prepared to return to the sea despite the fondness he'd come to hold for Bilgewater. As he stood at the docks, a massive dragon-shark attacked the port. Fizz defeated the beast, using his resourcefulness and knowledge of the creatures' weaknesses to his advantage. Having earned the gratitude and respect of the humans, Fizz decided to stay in Bilgewater. He joined the League of Legends to further serve his new home.
Source: The Game Website.