Apostle, and Bishop of Milan
Barnabas was, according to tradition, one of the prominent Christian disciples in Jerusalem. According to Acts 4:36, Barnabas was a Cypriot Jew (a native of Cyprus and a Levite).
He is first mentioned in the Acts of the Apostles as a member of the early Christian community in Jerusalem, who sold the land that he owned and gave the proceeds to the community.
When the future Paul the Apostle (who had been a persecutor of Christians) returned to Jerusalem after his conversion, Barnabas introduced him to the apostles. They may have been fellow students in the school of Gamaliel.
The disciples were understandably skeptical about Paul. It was Barnabas who advocated for him and encouraged others to forgive him. Barnabas is, therefore, considered the patron saint of second chances.
Barnabas was named an apostle in Acts 14:14. He and Paul undertook missionary journeys together and defended Gentile converts against the Judaizers. They travelled together making more converts (c. 46–48), and participated in the Council of Jerusalem (c. 49). Barnabas and Paul successfully evangelized among the “God-fearing” Gentiles who attended synagogues in various Hellenized cities of Anatolia.
Although the date, place, and circumstances of his death are historically unverifiable, Christian tradition holds that Barnabas was martyred at Salamis, Cyprus. He is traditionally identified as the founder of the Cypriot Orthodox Church. His feast day of Barnabas is celebrated on June 11.
He is venerated in the Catholic Church, Eastern Orthodox Church, Oriental Orthodox Churches, Anglican Communion and Lutheran Church.
(Various sources including Wikipedia)