Before Order 66
Much like the anime source Shark Tale, Will Smith Fish has very much the same origin as he does in the movie. He is shown to be a whale washer, who wishes to be powerful, but ends up losing his money and nearly getting eaten by a shark, which he ends up accidently killing. He is then named the Sharkslayer and is given fame and fortune. After this he is adopted by Big Daddy Fish to be his son. Later on, he decides to fake the death Don Lino's son Lenny to make him his bodyguard
and bitch so he can take more benefit and faith of being a true Sharkslayer.
He, Lenny and Big Daddy visit Don Lino and Oscar decides to execute Order 66 killing all sharks in the world only to prove his point to Don Lino who is left as the only survivor along with Lenny (although they later die anyway). Oscar rises to power proclaiming himself the emperor of the ocean and the series takes a dark turn from then with Oscar now in control of the ocean and its people.
After Order 66
It is later revealed that a baby shark was adopted by Glumgold, shortly after Order 66, and serves as the last remaining shark in the ocean. Oscar learns of this and plans to kill Glumgold and the baby shark to ensure there are no more sharks in the ocean. He is seen at the end of YTP: Scrooge McDank Plots to Assassinate Mark Zuckerbeak, watching Glumgold very closely. Big Daddy Fish asks if he can give the order to kill him, but Oscar stops him by saying he has a better idea.
He is later called by Mrs Claus to kill Heat Miser, which he claims is the favorite part of the game. Oscar sends the Death Star's Ice Beam Laser to kill Heat Miser, who claims himself to be a god, so he can never die. Heat Miser barely manages to survive the attack, only to end up being finished off by Oscar, who cruses him with a wooden beam. Taking over Heat Miser's land and forming his own new empire, Oscar proclaims that the land snow, like it did so long ago.
The Crucification of Glumgold and the Extinction of all Sharks
Oscar is shown framing Glumgold for stealing the Oyster's Pearl, which caused the Oyster to go on a mad rampage across Bikini Bottom. Glumgold tries to plead his innocence but the crowd doesn't believe his words. Scrooge McDuck apprehends Glumgold, and asks what he says in his defense. Glumgold tells Scrooge of Oscar's takeover of the ocean, but Scrooge believes that it is just nonsense, implying that the Takeover of the Ocean was quite a well hidden secret that nobody knew except for Glumgold, and Oscar and his men. Glumgold is then crucified by the people of Bikini Bottom for stealing, with Oscar looking on in satisfaction. After Glumgold is crucified, Oscar's men ask what they are going now, to which Oscar replies that they do something they should have done a long time ago, kill the last shark in the ocean, which Oscar succeeds in doing, rendering all sharks in the ocean extinct.
Tamatoa, not happy with Oscar's rule of the ocean, kidnaps (and possibly adopts) Jack Jack to attempt to use to kill Oscar and rule the ocean himself.