The Chronicle of Matthew of Edessa records that "Thoros son of Hethum" was installed as governor of Edessa by Tutush, who had defeated and killed emir Bouzan in the year 543 of the Armenia era (26 February 1094 - 25 February 1095). According to Sturdza, Hethum was descended from the Pahlavouni, an important family in Caucasian Armenia.
Thoros was a former officer (curopalates) in the Byzantine Empire and a lieutenant of Philaretos Brachamios. He was Armenian but practiced the Greek Orthodox faith. He conquered land to the east of that conquered by his fellow Armenian Rupen.
Around 1094, the Seljuk emir of Damascus, Tutush I, captured Edessa and established Thoros as governor.
Thoros immediately tried to take control of the city for himself. When Yaghi-Siyan, emir of Antioch, and Ridwan, emir of Aleppo, took refuge in Edessa after being defeated by Malik Shah I, Thoros tried to take them captive and ransom them.
The other Edessan nobles did not agree with this and they were freed. Thoros then fortified Edessa and cut off the citadel, garrisoned by Turkish and Armenian troops.
The Turks and Ortoqids besieged the city for two months, but were unable to capture it even after breaking through the walls.
The Turks withdrew and Thoros was recognized as lord of the city. As a Greek Orthodox Christian, he was not well loved by his Armenian subjects in Edessa. He resisted attacks from the Seljuks, but in 1098 had to ask for help from the crusaders, who were occupied at the siege of Antioch.
Baldwin of Boulogne had come to Edessa rather than participate in the siege, probably looking to carve out some territory for himself, and had captured Turbessel.
Thoros invited him to Edessa and made an alliance with him in February 1098. Thoros agreed to let him have the city and made plans to flee with his family to Melitene, but shortly afterwards, on March 9, Thoros was assassinated by the Armenian inhabitants of the city, possibly at Baldwin"s command, and Baldwin became the first count of Edessa.
