Muhammad Yaqub Bek was a [Turkic peoples] adventurer who became head of the kingdom of Kashgar

Kashgar

Kashgar or Kashi is an oasis city with approximately 350,000 residents in the western part of the Xinjiang Uyghur Autonomous Region of the People's Republic of China. Kashgar is the administrative centre of Kashgar Prefecture which has an area of 162,000 km² and a population of approximately...

ia.
In English-language literature, the name of Yaqub Beg has also been spelt as Yakub Beg (Encyclopædia Britannica

Encyclopædia Britannica

The Encyclopædia Britannica , published by Encyclopædia Britannica, Inc., is a general knowledge English-language encyclopaedia that is available in print, as a DVD, and on the Internet. It is written and continuously updated by about 100 full-time editors and more than 4,000 expert...

), Yakoob Beg (Boulger, 1878), or Ya`qūb Beg (Kim Hodong, 2004). Authors using Russian sources have also used the spelling Yakub-bek (Paine, 1996).
A few publications in English written by Chinese authors spell his name Agubo, which is the Pinyin

Pinyin

Pinyin is the official system to transcribe Chinese characters into the Roman alphabet in China, Malaysia, Singapore and Taiwan. It is also often used to teach Mandarin Chinese and spell Chinese names in foreign publications and used as an input method to enter Chinese characters into...

 transcription of the Chinese transcription of his name, 阿古柏.

The first name, Muhammad, is subject to the usual variations in spelling as well.
Yakub Beg was born in the town of Pskent, in the Khanate of Kokand

Khanate of Kokand

The Khanate of Kokand was a state in Central Asia that existed from 1709–1883 within the territory of modern eastern Uzbekistan, southern Kazakhstan, Tajikistan and Kyrgyzstan...

 (now Piskent in the Tashkent Province of Uzbekistan

Uzbekistan

Uzbekistan , officially the Republic of Uzbekistan is a doubly landlocked country in Central Asia and one of the six independent Turkic states. It shares borders with Kazakhstan to the west and to the north, Kyrgyzstan and Tajikistan to the east, and Afghanistan and Turkmenistan to the south....

).