Bali, son of Virochana, was pushed to underworld by Vamana. My understanding was he rules there with Vishnu serving as his door keeper.
In Mahabharata, a story narrated where Bali was born as ass. When Indra asked Brahma where is Bali, Brahma says
Vali may now have taken his birth among camels or bulls or asses or horses, and having become the foremost of his species may now be staying in an empty apartment.
Indra then goes looking for him and funds him in apartment as an ass.
Question is, why did Bali get birth as an ass? How can he get another birth if he is ruling where Vamana pushed him?
[Edit] This gets even more interesting as Bali then kind of challenges Indra that he will be come back with more power and takeover everything once again.
At present the Sun shines as much in the east as in the west, and as much in the north as in the south. When, however, the Sun, withdrawing himself from all sides, will shine only upon the region of Brahman situated in the middle of Sumeru, then will again occur a great battle between the gods and the Asuras, and in that fight I shall certainly vanquish all of you. When the Sun, withdrawing himself from all sides, will shine fixedly upon only the region of Brahman, then will again occur a great battle between the gods and the Asuras, and in that fight I shall surely conquer all of you.
Bhisma, who was narrating this to Yudhistita, concludes that:
Thus addressed by Indra, O Bharata, Vali, the chief of the Daityas, proceeded towards the south.
The footnote from Ganguli says Bali will return for this fight in Savarnika Manwantara (next one).
==== My questions remains same: why Bali became an ass; how come Bali returns for another war with Gods and Asuras. The puranas say he will be next Indra?