Onesiphorus (Greek Onēsiphoros, 'helpful, profitable') was a Christian of Ephesus to whom Paul gives extended thanks in 2 Timothy 1:16–18 — the only passage in the New Testament addressed to him. Paul writes from his final Roman imprisonment (the second imprisonment, c. AD 66–67, immediately before his martyrdom): 'The Lord give mercy to the house of Onesiphorus, because he hath often refreshed me, and hath not been ashamed of my chain: but when he was come to Rome, he carefully sought me, and found me.'
The passage is extraordinarily personal: Paul singles out Onesiphorus as the one Christian who, when Paul was imprisoned in Rome under capital sentence and other Asia Minor Christians had withdrawn from association with the condemned apostle (2 Timothy 1:15 — 'all they who are in Asia are turned away from me'), travelled from Ephesus to Rome specifically to find Paul and visit him in the Mamertine Prison, undeterred by the danger of association with a condemned criminal.
Paul's prayer 'The Lord give mercy to the house of Onesiphorus' (2 Timothy 1:16) and his prayer in 2 Timothy 1:18 ('The Lord grant unto him to find mercy of the Lord in that day') has been read since the patristic period as evidence that Onesiphorus had died between Paul's first contact with him and the writing of 2 Timothy — making this one of the few clear New Testament texts on Catholic intercessory prayer for the dead. Byzantine tradition makes him Bishop of Colophon or of Cyrene, and identifies him as one of the Seventy.