Berthold II von Katzenelnbogen

1199–1217) was a German nobleman of the family of the Counts of Katzenelnbogen[a] and a participant in the Fourth Crusade (1202–04), who became lord of Velestino (c.1205–17) and regent of the Kingdom of Thessalonica (c.1217) in Frankish Greece.

Disappointed with the political disunity and civil war in the Holy Roman Empire[d] in the aftermath of Philip's 1198 election as king, Berthold joined the Fourth Crusade in 1202.

In 1203, when the Crusader army reached Constantinople, capital of the Byzantine Empire, the German contingent was under the overall command of Henry of Flanders, with whom Berthold developed a good relationship.

[2] On 12 April 1204, after the breach of Constantinople by the Crusaders, a certain German count (quidam comes theothonicus), possibly Berthold, set fire to a section of the city in order to force the defending Byzantines to retire.

[1][3] In 1205, he was sent by Pope Innocent III to a diplomatic mission in Asia Minor to mediate in a dispute between King Leo II of Armenia and Prince Bohemond IV of Antioch.

In the meantime, Boniface of Montferrat had been killed fighting against the Bulgarians, and had left his underage son Demetrius as his heir, with the latter's mother, Margaret of Hungary, as regent and Count Oberto II of Biandrate as guardian (baiulus) of the kingdom.

In 1211, however, the Latin archbishop of Heraclea Perinthus complained to Pope Innocent III that Berthold forcefully kept Margaret in his possession, and that he had misappropriated lands belonging to the church of Hagia Sophia in Thessalonica.

[1] The wording of these papal letters has engendered confusion over whether Berthold was himself the "imperial bailiff" (balivus imperatoris) the pope was addressing or else merely the lord of Velestino.

[8] Berthold is explicitly mentioned as regent—baiulus regni Thessalonicensis[g]— only once: in a letter of 21 April 1217 from Pope Honorius III, notifying him of his appointment of Giovanni Colonna as papal legate to Thessalonica.