Galdan Boshugtu Khan (1644 – 3 May 1697) was a Choros-Oirat khan of the Dzungar Khanate. As fourth son of Erdeni Batur, founder of the Dzungar Khanate, Galdan was a descendant of Esen Taishi, the powerful Oirat Khan of the Northern Yuan dynasty who united all Mongols in the 15th century. Galdan's mother was a daughter of Güshi Khan, the first Khoshut-Oirat King of Tibet.

At the age of 7, Galdan was sent to Lhasa to be educated as a lama under the 5th Dalai Lama at Tashilhunpo Monastery. He spent 20 years studying Buddhist canons, philosophy, astronomy, astrology and basics of medicine and pharmacology. In this sense, he was one of the best educated kings in Mongolian history.

He backed his brother Sengge's claim to the title Khan of the Dzungars against the pretensions of their half-brothers Chechen Tayiji and Zotov Batur. With the support of Ochirtu Khan of the Khoshut, Sengge solidified his rule in 1661. Nevertheless, the two brothers never gave up their royal aspirations, and in 1670 Chechen Tayiji murdered Sengge in a family coup. When Galdan's mother Amin-Dara arrived to Lhasa to inform Galdan of Sengge's death, Galdan immediately renounced his status as a lama and quickly returned to the Irtysh Valley to avenge him. After soundly defeating Chechen Tayiji and Zotov Batur in 1671, the Dalai Lama named Galdan Khong Tayiji "Crown Prince".

After Sengge's death, Galdan took his widow Anu-Dara, granddaughter of Ochirtu, as his bride. Conflict within the family soon erupted again when Ochirtu, fearing Galdan's popularity, supported Galdan's uncle and rival Choqur Ubashi. In 1678 Galdan forced Ochirtu to flee to Kokonur and established hegemony over the Oirats. The following year, the Dalai Lama bestowed on him the highest title of Boshoghtu (or Boshughtu) Khan, or "Divine Khan".

Imams of the Naqshbandi lineage had replaced the Chagatayid Khans in the early 17th century. After the defeat of the White Mountain Khoja [zh], their exiled ruler Afaq Khoja approached the 5th Dalai Lama for military assistance in 1677. By the request of the latter, Galdan overthrew the Black Mountain Khoja [zh] in the Dzungar conquest of Altishahr and installed Afaq as his client ruler there. Galdan decreed that the Turkestanis would be judged by their own law except in cases affecting the Dzungar Khanate. The Dzungars kept control over the Tarim Basin until 1757.

In 1680 the Black Kyrgyz raided Moghulistan and occupied Yarkant. The inhabitants of Yarkant appealed to Galdan Khan for help. The Dzungars conquered Kashgar and Yarkant and Galdan had its ruler chosen by its inhabitants. Then he invaded the north of Tengeri Mountain in modern Kazakhstan the next year; he defeated Tauke Khan's Kazakhs but failed to take Sayram. He conquered Turfan and Hami the next year. In 1683 Galdan's armies under Rabtan reached Tashkent and the Syr Darya and crushed two armies of the Kazakhs. After that Galdan subjugated the Black Khirgizs and ravaged the Fergana Valley. From 1685 Galdan's forces aggressively pushed the Kazakhs. While his general Rabtan took Taraz, and his main force forced the Kazakhs to migrate westwards.

In 1687, he besieged Turkistan, an important pilgrimage center for the Muslim Kazakhs, but could not take it.

At first the Khalkha and Oirat Mongols were allies, bound by the provisions of the Mongol-Oirat code. To cement this union, Galdan attempted to ally with Zasaghtu Khan Shira who lost part of his subjects to Tushiyetu Khan Chakhun Dorji, and moved his orda near the Altai Mountains. Tushiyetu Khan attacked the right wing of the Khalkhas and killed Shira in 1687. Galdan dispatched troops under his younger brother Dorji-jav against the Tushiyetu Khan the next year, but they were eventually defeated and Dorji-jav was killed in the ensuing battle. Chakhundorji murdered Degdeehei Mergen Ahai of the Zasaghtu Khan who was on the way to Galdan. The Qing court intervened and called all the Mongolian nobles to assemble a conference.