St. Aristobulus, a Jewish native of Cyprus, was numbered among the Seventy Disciples appointed by Our Lord (St. Luke 10). He is said to have been the brother of St. Barnabas and father-in-law to St. Peter and to have accompanied St. Paul on his missionary journeys. He is mentioned by the Apostle Paul in the Epistle to the Romans (Rom 16:10). Along with the Disciples Urban (bishop in Macedonia), Stachys (first bishop of Byzantium), Narcissus (bishop of Athens), Apelles (bishop of Heraclea in Trachis), and Amplias (a Roman Christian), he assisted St. Andrew the Apostle.
According to legend, having first visited the Celtic tribes of Northern Spain, he preached the Gospel in Britain and became its first bishop.
The Greek Martyrologies read: "Aristobulus was one of the seventy disciples, and a follower of St. Paul the Apostle, along with whom he preached the Gospel to the whole world, and ministered to him. He was chosen by St. Paul to be the missionary bishop to the land of Britain, inhabited by a very warlike and fierce race. By them he was often scourged, and repeatedly dragged as a criminal through their towns, yet he converted many of them to Christianity. He was there martyred, after he had built churches and ordained deacons and priests for the island."
Haleca, Bishop of Saragossa, attests: "The memory of many martyrs is celebrated by the Britons, especially that of St. Aristobulus, one of the seventy disciples (Halecae Fragments in Martyr.)."
In 303, St. Dorotheus of Tyre in his Acts of the Seventy Apostles wrote, "Aristobulus, who is mentioned by the Apostle in his Epistle to the Romans, was made bishop in Britain."
He is attested to as bishop of Britain by Pseudo-Hippolytus.
The Adonis Martyrologia of St. Ado, Archbishop of Vienne in Lotharingia, under March 17 reads, "Natal day of Aristobulus, Bishop of Britain, brother of St. Barnabas the Apostle, by whom he was ordained bishop. He was sent to Britain, where, after preaching the truth of Christ and forming a Church, he received martyrdom."
Revered by the Brythonic Celts, the saint lent his name to the medieval British kingdom of Arwystli (which continues to this day as a cantref within the county of Powys, Wales).
His feast days are celebrated on March 16, on October 31 (with SS. Amplias, Apelles, Stachys, Urban, and Narcissus), and on January 4 with the Seventy.