Thaddeus (Greek Thaddaios) is one of the Twelve Apostles of Jesus referred to in Matthew and Mark. In Luke 6:16 and Acts 1:13 his name is replaced with "Judas the son of James", indicating that Thaddeus might be a family name. The manuscript of the King James Version identifies "Lebbaeus, whose surname was Thaddeus" in Matthew 10:3. This ambiguity about Thaddeus's identity has led to speculations that he may be one of the seventy Jesus sent out after His Ascension rather than one of the Twelve. In the Catholic tradition, however, he is considered synonymous with Saint Jude, often referred to as Saint Jude Thaddeus. St. Thaddeus along with St. Bartholomew brought the new religion of Christianity to Armenia in the first century. Thus the Armenian Church is called the Armenian "Apostolic" Church, since the two apostles were the first to bring the new faith to Armenia.
A famous legend involving the apostle Thaddeus was recorded by Eusebius of Caesarea. King Abgarus of Edessa wrote to Jesus, asking him to come cure him of an illness. Instead, Thaddeus is said to have come, bearing a cloth featuring Jesus' facial features, by the virtues of which the king was miraculously healed. This relic became known as the Image of Edessa, which some modern researchers believe is misinterpreted today as the Shroud of Turin.
Some believe Thaddeus to be the author of Epistle of Jude, but this has been subject to debate by biblical scholars throughout the centuries.
Thaddeus is alternatively spelled "Thaddæus" or "Thaddaeus" in different versions of the Bible.