Wikipedia
Madhu and Kaitabha , Rakshasass or demons of Hindu mythology, are associated with Hindu religious cosmology. They both originated from one of the ears of God Vishnu, while he was in the deep sleep of Yoganidra. From his navel, a lotus has sprouted out on which Brahma, the creator, was sitting and contemplating to create the cosmos.
Bhagavata Purana states that during the creation, the demons Madhu and Kaitabha stole the Vedas from Brahma and deposited them deep inside the waters of the primeval ocean. Vishnu, in his manifestation as Hayagriva, killed them, and retrieved the Vedas. The bodies of Madhu and Kaitabha disintegrated into 2 times 6 — which is twelve pieces (two heads, two torsos, four arms and four legs). These are considered to represent the twelve seismic plates of the Earth.
According to another legend, Madhu and Kaitabha are considered (demons), designed to annihilate Brahma. However, Brahma spotted them, and invoked the goddess Mahamaya. At this point, Vishnu awoke, and the two conspiring demons were killed. This led to Vishnu being called Madhusudanah - the killer of Madhu.