John X, whose father’s name was also John, was born at Tossignano, along the river Santerno. He was made a deacon by Peter IV, the bishop of Bologna, where he attracted the attention of Theodora, the wife of Theophylact I of Tusculum, the most powerful noble in Rome. John was a relative of Theodora's family. Liutprand of Cremona alleged that John became her lover during a visit to Rome; However, Johann Peter Kirsch says, "This statement is, however, generally and rightly rejected as a calumny. Liutprand wrote his history some fifty years later, and constantly slandered the Romans, whom he hated. At the time of John's election Theodora was advanced in years, and is lauded by other writers (e.g. Vulgarius)."