Dakuwanga

In Fijian mythology (specifically: Fiji), Dakuwaqa is a shark-god. He was greatly respected by fishermen because he protected them from any danger at sea and sometimes protected them from evil denizens of the sea. He was once going inland to conquer Kadavu through the river when another god challenged him. He was in the form of an octopus and after a great battle, the octopus won (mainly due to his 8 arms which enabled him to hold off the massive shark god's attack) forcing Dakuwaqa to promise to never attack the island of Kadavu again. That is how, Dakuwaqa became the god and protector of Kadavu. Dakuwaqa can also change shape into anything, but his real form is that of a muscular Fijian man with the upper torso of a shark.
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[Polynesian] The Fijian shark-god. He is the scourge of the fishermen, eating their fish as well as the men who fall overboard. However, ever the powerful shark-god one day met his match, the giant octopus, guardian of the reef. After a long battle, the octopus won and the Dakuwanga had to promise never to attack the men of the Kandavu (one of the major Fijian islands) again.