Chitraketu is reborn as Vritrasur

 Srimad Bhagavatam - Birth of Demon Vritrasura

Why did Twasta, the father of Vishwarupa, perform a yagna and was the outcome? Who is Chitraketu?

Vritasur was born as the son of Twasta. Vritasur, in his previous birth as Chitraketu, a gandarva, was cursed by Goddess Parvathi to be born as a demon.

Vritrasura was born as a demon and grew up dangerous day by day. The whole world was shocked by his statute. Indra and other gods approached Mahavishnu for help.

Mahavishnu directed them to Sage Dadichi through him alone Vrithasur can be defeated. Sage Dadichi, through his austerity, had earned a boon that his bones would be as strong as vajra (diamond). 

Upon sacrificing his body, Vajrayuda (a divine weapon ) is made using his ashes. Viswakarma, architect of gods, facilitated in making this weapon to Indra.

Source: Bhagavatha Mahapurana