Recently named a Saint after returning from a noble mission to the eastern Stardust Pass, the safest route to Varago from Crusche that passes through the dangerous Downside
Born an orphan and raised by Ilmatari priests in Crusche Proper
Met Maria Dorado de la Rosa as a child in the Sonnerie and became friends, though that friendship is now challenged
Loves fruit and sweet things
Marked by Bhaal as a young boy after the murder of his parents. Father Pietro knows this, and was trying to reform him to show that even one claimed by Bhaal can be redeemed by the Hands of Ilmater
This is extra important to Pietro, who was spurned by the betrayal of his closest companion in the priesthood, Judas' uncle Marcus
Marcus and [Judas' mom] are distant descendants of Gehenna, an ancient Bhaalist who dueled with Ilmater during the Calamity, and who was restored in unholy ritual shortly before the Ruidian Collapse
He is a poor priest inwardly, despite being very exact outwardly. He has a temper and a violent streak, and sees himself superior to many among the church's ranks, especially those who do not follow its teachings to the letter.
Motivations
He wants to discover his own path, whether that leads further into the church, far away from it, or whether he makes peace with its teachings and lives them in his own way on his own journeys.
This will largely be influenced by the journey at hand.