Vritra was King Chitraketu in his previous life, childless despite 10 million women.
He prayed to sage Angiras, a queen gave birth to Kritadyuti, he was killed by the other jealous women. Angiras brought him back to life.
Chitraketu went into meditation and became a Gandharva. One day he saw Parvati sitting on Shiva’s lap and laughed. Parvati cursed him to become a demon in the next life. He was born as Vritra.