Pier Leoni (or Pierleone) (Latin: Petrus Leo or Petrus filius Leonis) (died 2 June 1128) was the son of the Jewish convert Leo de Benedicto and founder of the great and important medieval Roman family of the Pierleoni.
He was one of the regents of the city itself when Pope Paschal II left in 1108 to deal with raising troops.
In 1111, Pierleone negotiated the imperial coronation of the Emperor Henry V. Ever a faithful ally of the pope, in 1117, he retook Rome for him, but was subsequently holed up in his tower by Ptolemy I of Tusculum.
Pierleone held the Theatre of Marcellus, Tiber Island, and the Castel Sant'Angelo, fortress of the popes.
Of these children, he left several sons: Leo, Peter (later Antipope Anacletus II), Jordan (later Patrician of the Commune of Rome), Roger, and Huguizon.