Pope Saint Hyginus was bishop of Rome from about 136 or 138 to about 140 or 142. Tradition holds that during his papacy he determined the various prerogatives of the clergy and defined the grades of the ecclesiastical hierarchy. However, modern scholars tend to doubt this claim and view the governance of the church of Rome during this period as still more or less collective.

According to the Liber Pontificalis, Hyginus was a Greek born in Athens. The source further states that he previously was a philosopher, probably founded on the similarity of his name with that of two Latin authors.

Irenaeus says that the Gnostic Valentinus came to Rome in Hyginus's time, remaining there until Anicetus became pontiff (Against Heresies, III, iii). Cerdo, another Gnostic and predecessor of Marcion, also lived at Rome in the reign of Hyginus; by confessing his errors and recanting he succeeded in obtaining readmission into the bosom of the Church, but eventually he fell back into the heresies and was expelled from the Church. How many of these events took place during the time of Hyginus is not known.