Pope Liberius
Pope Liberius (310 – 24 September 366) was the bishop of Rome from 17 May 352 until his death. According to the Catalogus Liberianus, he was consecrated on 22 May as the successor to Pope Julius I. He is not mentioned as a saint in the Roman Martyrology. That makes him the earliest pontiff not to be venerated as a saint in the Roman Rite and one of only two popes to be omitted from Roman Catholic sainthood in the first 500 years of church history. (Pope Anastasius II is the second.)
Liberius is mentioned in the Greek Menology, the Eastern equivalent to the martyrologies of the Western Church and a measure of sainthood prior to the institution of the formal Western processes of canonization.