Svarbhanu

A demon who took the form of a God and sat in line with the Gods when the nectar of immortality, Amrita, was distributed.

Surya and Chandra recognized him and Vishnu cut off his head.

But Svarbhanu had already swallowed the Amrita, body and head remained alive. The head became Rahu, the body Ketu, they are the lunar knots.