Who was Barnabas?

He was originally a Levite named Joseph who converted in Jerusalem and became the apostle Paul's companion on most of his first missionary journey. They ended up going different directions when they had a dispute over whether they should take John Mark or not (Barnabas wanted to, Paul didn't). Barnabas took Mark and sailed for Cyprus, but Paul choose Silas and continued on his journey.

Acts 15:

³⁶And some days after Paul said unto Barnabas, Let us go again and visit our brethren in every city where we have preached the word of the LORD, and see how they do. ³⁷And Barnabas determined to take with them John, whose surname was Mark. ³⁸But Paul thought not good to take him with them, who departed from them from Pamphylia, and went not with them to the work. ³⁹And the contention was so sharp between them, that they departed asunder one from the other: and so Barnabas took Mark, and sailed unto Cyprus; ⁴⁰And Paul chose Silas, and departed, being recommended by the brethren unto the grace of God. ⁴¹And he went through Syria and Cilicia, confirming the churches.

You can read about Barnabas in Acts 14:8-20

Barnabas The Apostle of Encouragement - A Study of Acts 15:35-41

  An Educational Bible Lesson from Garden of Praise