Lord Delarin

WARNING!!! MAJOR SPOILERS AHEAD!!! Lord Delarin is the main antagonist of Kaeru no Tame ni Kane wa Naru. He is the leader of the Croakians, who take over the Mille-Feuille Kingdom. He is secretly a snake that plans to devour the frogs within the kingdom and marry Princess Tiramisu.

Story
Lord Delarin commands his Croakians to invade the Mille-Feuille Kingdom, and they successfully seize the castle. Within, he falls into a deep slumber, as his minions terrorize the kingdom's people, round up frogs to feed to him, and try to find the missing Princess Tiramisu to wed her to him.

He isn't seen officially until the end of the game, where the Prince of Sablé confronts him, wielding the Snake Killer. While Delarin rests, despite his loud snores, he appears simply as a tiny snake. The Prince easily beats him up, but may choose to either slay or spare him. Slay, because Delarin is evil, or spare, because the Prince feels bad for beating up such a tiny snake.

No matter what he chooses, however, the tiny snake will suddenly morph into a giant, towering snake. The Prince will attempt to fight him, but will use the Z-Flute to summon the Mad Scienstein within the Igari Z to help himself out. This ends up helping both Delarin and the Prince, as the Igari Z performs a healing dance to restore both of their health.

Lord Delarin then knocks the Igari Z out of the way, and zeroes in on the Prince. But, suddenly, Prince Richard and his men appear! Despite being frogs, they bravely attack the giant snake, who ends up eating them one by one. As Prince Richard is about to sacrifice himself, the Prince of Sablé refuses to let him, and the snake advances upon them. Just as he is about to kill them, the Spring Bell suddenly chimes!

Prince Richard turns back into a human, and within Lord Delarin, the Custard Soldiers turn into humans and begin to attack him from the inside. Lord Delarin spits them out with ease, however, and summons a barrier to protect himself. Prince Richard and the Prince of Sablé are backed into a corner, but they are saved by a sudden sword being thrown into Lord Delarin's eyes, blinding him and creating a hole in his barrier!

The sword was thrown by Alfred Jinbee, who commands the Prince of Sablé to strike with the Snake Killer once more! Now powered up by the power of friendship by Prince Richard's presence, the sword is able to take down the giant snake, and the Prince of Sablé triumphs over Delarin. The snake, defeated, monologues about how he wished to make Princess Tiramisu his queen, become ruler of the Mille-Feuille Kingdom, and create an empire, before disappearing...

Etymology
Delarin could possibly be a corruption of "delicious".