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Janah ad-Dawla was the ArabSeljuq emir of Homs during the First Crusade. He was the atabeg of Ridwan who took control of Aleppo after the death of Ridwan's father Tutush I in 1095. He later joined Kerbogha's army during the second siege of Antioch in 1098. He was murdered by three Assassins in 1103, apparently by order of al-Hakim al-Munajjim and apparently instigated by Ridwan.
References
Baldwin, Marshall W., and Setton, Kenneth M, A History of the Crusades: Volume One, The First Hundred Years, 1969, pg. 164
Lewis, Bernard (2003). The Assassins: A Radical Sect in Islam. New York: Perseus Books Group., pg. 100