Undur Geghen Zanabazar (Mongolian: Өндөр Гэгээн Занабазар, Öndör Gegeeṅ Zanabazar, "High Saint Zanabazar"; 1635–1723), born Eshidorji (Ишдорж, Išdorj),^{[citation needed]} was the first Jebtsundamba Khutuktu, the spiritual head of Tibetan Buddhism for the Khalkha in Outer Mongolia. His name 'Zanabazar' is the Mongolian rendition of the Sanskrit 'Jnana-vajra' meaning thunderbolt (vajra) of wisdom (jnana).^{[citation needed]} Etymologically this name would be equivalent to 'known-vigor' in English, a language genetically related to Sanskrit.

Zanabazar was born as a son of Tüsheet khan Gombodorj – at that time one of the three khans in Khalkha – and his wife, Khandojamtso. Zanabazar became a religious leader in eastern Mongolia. In that time western Mongolia had gained in power under Galdan Boshogtu Khan. Galdan Boshogtu, not descended from the Golden Lineage (Genghis Khan), tried to unite all the Mongolian states and take the throne for himself. Zanabazar declined all the western Mongols' proposals. Finally Galdan Khan decided to reunite the Mongol states by force and collaborated with rising power on the north Russia and in south Manchus against eastern Mongolia. Thousands of warriors from the western Mongol Empire went to war with eastern Mongolia. When Galdan Khan's army came to the area where today the city of Ulan Bator is located, conducting two wars in front, on the north with Russia on the west with Galdan Boshogtu, Zanabazar escaped to southern Mongolia. The Manchus were interested in defeating both Mongolian states, and this gave them an incredible chance to accomplish that goal. The Manchu army went to war with the Western (Oirad) Mongol Empire, Zanabazar's goal. After the battle at Zuun Mod (near present-day Ulan Bator) the Oirad Mongol warriors were defeated and went back to the west. Zanabazar became a religious leader in Mongolia while his native land (Eastern Mongolia) fell to and became a vessel of the Manchus.