pope from c. 199 to 217.

Of humble birth, he succeeded Pope St. Victor I and is believed to have appointed his own successor St. Calixtus I (Calixtus I, Saint) (Callistus) as his chief deacon. During Zephyrinus' pontificate, the Roman priest St. Hippolytus vigorously opposed the spread of Monarchianism, a Trinitarian heresy that affirmed the sole deity of God the Father. Zephyrinus failed to condemn Monarchianism or favour the Logos doctrine (emphasizing the distinction of the Persons of the Trinity), of which Hippolytus was the passionate champion. Opposing Zephyrinus, Hippolytus thus started the first schism in the history of the Christian Church.

Unfortunately, the primary source of information on Zephyrinus is Hippolytus' Philosophoumena, in which he describes the Pope as a weak man “unskilled in the church's rule” and dominated by Calixtus. Hippolytus considered both men culpable for being unwilling to enter the theological debate on the Trinity. Zephyrinus died during the persecution of Christians that was instigated by the Roman emperor Lucius Septimius Severus.