Character and legend from the Ramcharitmanas.

Firstborn son of Satyaketu, king of Kaikaya, his younger brother’s name was Arimardan.

When Pratapbhanu was king, he ruled together with his brother. Their minister was Dharmaruchi.

Pratapbhanu subdued to all kings. One escaped into the woods and sought revenge.
Likewise did demon Kalaketu, whose family Pratapbhanu had wiped out.
King and demon teamed up.

When Pratapbhanu was chasing a boar (the demon), he got lost in the forest and came to the hermitage of a sage (the defeated king). The sage prepared a feast for him, attended by Brahmins. The cook was the demon, he mixed the meal with human flesh. When the brahmins found out about this, they cursed Pratapbhanu for being born as a demon. That demon was Ravana. Arimardan became Kumbhakarna.

According to the ‚classical‘ legend, Ravana and Kumbhakarna are Vishnu’s reborn gatekeepers.

Read about Pratapbhanu here