Chagatai is an extinct Turkic language that was spoken in Central Asia, particularly in the Khorasan region. It was also spoken by the early Mughal rules of India. It was used as a shared literary language until the early 20th century.
The name Chagatai comes from the Chagatai Khanate (1225-1680s), which was established by Chagatai Khan, the second son of Genghis Khan.
Chagatai is a member of the Karkluk branch of Turkic languages and contains many loanwords from Arabic and Persian. It descended from Old Turkic, and its written form was based on Karakhanid and Khorezmian, two Middle Turkic literary languages.
In Uzbekistan, which was founded as the Soviet Republic of Uzbekistan in 1924, Chagatai is officially known as 'Old Uzbek'. In China it is sometimes called 'Ancient Uyghur'. Uzbek and Uyghur are indeed closely related to Chagatai.
Details of the Chagatai alphabet supplied by Michael Peter Füstumum
Information about Chagatai