Poseidon intended her to use her lovely voice to lure pirates to their deaths in order to avenge Ursula's mother's murder at the hands of an unnamed pirate.

Ursula declined and instead befriended Captain Hook, a pirate who shared her quest for independence. Ursula and Hook's friendship was shattered when Hook locked Ursula's singing voice inside an enchanted shell as a punishment for Poseidon destroying a weapon Hook desired.

Ursula was enraged and disappointed by both merfolk and humans, so she used Poseidon's trident to turn her hair into tentacles.