Thessalus was an eminent tragic actor (hypocrites) in the time of Alexander the Great, whose especial favour he enjoyed, and whom he served before his accession to the throne, and afterwards accompanied on his expedition into Asia.
[1] He acted as the envoy of Alexander to Pixodarus of Caria in 336 BC.
Early in 331 BC, he was defeated by the actor Athenodorus, much to Alexander's dismay.
[2] Thessalus later performed at the Susa weddings (324 BC).
Dictionary of Greek and Roman Biography and Mythology.