Onesimus was the slave that fled from his master to Rome and met the apostle Paul. Paul converted Onesimus to Christianity. He is the basis of Paul's letter "Philemon." Philemon was Onesimus' master. Paul sent Onesimus back to his master, asking him to be welcomed willingly, not just as a slave, but as a brother in Christ. Paul in his letter to Philemon offers to pay for any injustice that Onesimus might have done. Onesimus means "useful."
Next person in the Bible: Onesiphorus