The Acts of Thaddeus is a sixth-century story that expands on an earlier Syriac writing from the fifth century called the Doctrina Addaei (also known as the Legend of Abgar). That legend claims to record an exchange of letters between Abgar, the king of Edessa (AD 9–46), and Jesus. Because of this exchange, Jesus sends Thaddeus, one of his apostles, to visit Edessa.
In this story, Thaddeus performs many miracles, including healing King Abgar. However, in the Acts of Thaddeus, Abgar is healed earlier, when his messenger Ananias returns from seeing Jesus, before Thaddeus arrives. The Acts mainly describes Thaddeus’s work in establishing the church in Edessa.