Thaeron (also known later as Durthar Morgath) was a swordmaster who was employed by Lord Elmaer Oraun of Harrowdale during his reign for around five years between 1175 and 1185 DR (sources are not precise with dates). He died in the second inter-dale war in 1356 DR.
During the reign of Elmaer Oraun over Harrowdale, Thaeron was swordmaster. He disappeared, along with Elmaer and Elmaer's son Eramonn, during the Battle of Marak's Stile, in which Halvan the Dark seized control of Harrowdale, and it was rumoured that elven magic had prevented their deaths.
In 1351 DR, "fey blue mage-fire" was seen above a farm on a hill in Harrowdale, owned by three brothers, Torstan, Ulbaern and Durthar Morgath from Sembia. The next morning, the wizard Arauntan of Selgaunt reports that despite the brothers walking and talking in the same way, their appearances had become those of Erammon Oraun, Elmaer Oraun, and Thaeron.
In 1356 DR, during the second inter-dale war, Thaeron, or Durthar Morgath, depending on which account is to be believed, rallied troops from northern Harrowdale, before declaring himself "Thaeron, Rightful Swordmaster of Harrowdale", and was killed in the battle.