[1] His feast day is June 17, his name may also be spelled Raynerius, Rainerius, Rainier, Raineri, Rainieri, Ranieri, Raniero, or Regnier.

Rainerius was the son of Gandulfo Scacceri, a prosperous merchant and shipowner of Pisa, and Mingarda Buzzaccherini.

He met, through his travels, a holy man, Alberto, a nobleman from Corsica "who wore a cloak of animal hair, like a goat", and had entered the monastery of Saint Vitus (San Vito) in Pisa and become renowned for his work for the poor.

There he achieved fame and became a preacher,[4] being treated like a saint even in his lifetime, reputedly expelling demons and performing miracles.

In 1632 the Archbishop of Pisa, the local clergy, and the Pisan magistrates elected Rainerius as the patron saint of the city and the diocese.