The Evil Manta
The ancient inhabitants of Atlantica didn't seal this evil being in the darkest depths of the ocean for no reason. The Evil Manta is a high ranking agent who collects the souls of sea folk by spreading mistrust and lies through rumors of them being different. The resulting racial prejudice and wars following get him the souls he needs. Ariel managed to defeat him on several occasions before Ursula concocted her endgame. Eventually, the High Council realized that in order to defeat the Manta, who had long used the power of hate as his weapon, they would have to make him realize the power of love is far stronger than his hatred. So, they engineered the creation of a Little Evil through a retcon spell, hoping that with the prospect of a son in his possession, the Evil Manta would be able to reform more potently than before.