The brother of a sage named Yaja. The brothers lived on the banks of the Ganga. It was their yajna that brought to life Draupadi and Dhrishtadyumna. That story is thus –

Drona was the son of Bhardwaja. Prishata, the king of Panchala, and Bharadwaja were good friends. Prishata left his son Drupada with Bharadwaja for his education. Drona and Drupada studied together and after his studies, Drupada became the king of Panchala. When Drona visited him, Drupada ignored him. Drona was angry. He returned and taught the Pandavas and Kauravas in Hastinapura.  Drona later asked Arjuna to bring Drupada to him as a prisoner. Arjuna did that and Drupada was forced to give half the kingdom to Drona to free himself.

Drupada wished for a son who could avenge him. He requested Upayaja to conduct a yajna for him. He first refused but Drupada took care of him for a year and the sage finally agreed. Upayaja and Yaja went to Panchala and conducted the yajna. As per Mahabharata Adiparva Chapter 166 and Sabhaparva Chapter 80 verse 45, Dhrishtadyumna and Draupadi were born from this yajna.