Bakhtiyar Khalji  inaugurated Muslim rule in Bengal by conquering its northwestern part in early 1205 AD. A native of Garamsir (modern Dasht-i-Marg) in northern Afghanistan, Ikhtiyaruddin Muhammad Bakhtiyar Khalji belonged to the Khalj tribe of the Turks. He entreated Muhammad Ghuri at Ghazni to enlist him as a soldier but, because of his short physical stature with long arms extending below the knees, his prayer was rejected. A dejected Bakhtiyar proceeded to Delhi and sought an employment under Qutbuddin but there also his fate fared no better. Thence he went to Badaun where he was appointed to a lower post by Malik Hizbaruddin. From Badaun he repaired to Oudh and got a post befitting his ability under Malik Hushamuddin, the governor of the province. He was granted the parganas of Bhagwat and Bhuili in the district of Mirzapur as jagir. Soon a large number of Khalji adventurers gathered around him and with their help he carried on raids into the neighbouring territories.

In 1203 AD Bakhtiyar made a sudden dash against Bihar, occupied it and returned with enormous booty. He met Qutbuddin and gave him rich presents. Qutbuddin in turn received him with great honour. Turning now his attention towards Bengal Bakhtiyar started on his adventure in the winter of 1204-05 AD and, proceeding through the unfrequented Jharkhand region, marched so swiftly towards Nadia that only eighteen horsemen could keep pace with him. The city dwellers took him to be a horse-dealer and he captured the palace by surprise. Raja laksmanasena 'fled away by the back-door' bare footed. Meanwhile the main army of Bakhtiyar Khalji arrived and Nadia came under his possession.

Bakhtiyar Khalji stayed in Nadia for a short period and then marched upon Gaur (Lakhnauti). He conquered it without any resistance in 601 AH/1205 AD and made it the seat of his government. Afterwards he proceeded eastward and extended his authority over north Bengal. Bakhtiyar Khalji's territories extended from the modern town of Purnia via Devkot(in Dinajpur) to the town of Rangpur in the north, to the river Padma in the south, to the rivers Tista and Karatoa in the east and to the previously captured territory of Bihar in the west.

The last important event in the career of Bakhtiyar Khalji was his Tibet expedition. While he was making preparations for his expedition, a large portion of Bengal remained outside his kingdom. So, it is surprising that instead of conquering the remaining portions of Bengal, Bakhtiyar Khalji preferred to undertake such a hazardous campaign. There is no clear explanation about the motives underlying his project. It appears that Bakhtiyar Khalji's inordinate ambition or his desire to secure mastery over trade route from Tibet to Kamarupa and thence to Bengal or his intention to discover a short-cut route to Turkistan over Tibet impelled him to undertake this expedition.

Bakhtiyar collected necessary information about the routes leading to Tibet by sending there a few detachments. Ali Mech agreed to act as his guide through the hills. Before undertaking his Tibet expedition Bakhtiyar made adequate arrangements for the defence and administration of his kingdom. He created three big frontier governorships and posted Shiran Khalji, Ali Mardan Khalji and Husamuddin Iwaz Khalji at Lakhnur, Ghoraghat and Tanda respectively.

Bakhtiyar Khalji marched from Devkot with ten thousand horsemen up the river Bagmati in early 602 AH/1206 AD. Crossing the river over an ancient stone bridge he proceeded to the hills where, in a battle with the local people, he sustained heavy losses and decided to abandon the project. But the backlash was so hard that the return journey proved to be disastrous and he somehow reached Devkot with a little more than a hundred of his followers alive. At Devkot, Bakhtiyar Khalji fell seriously ill and when he was hovering between life and death, he was stabbed to death by Ali Mardan Khalji in 602 AH/1206 AD.

Bakhtiyar was a good administrator. He divided the kingdom into a number of districts and assigned them to the care of his principal nobles and military chiefs. They were entrusted with the duty of maintaining peace and order, collecting revenues, patronising learning and culture and looking after the moral and material well being of the people. Following the traditional principle he took steps to read the Khutbah and to introduce coins in his name. He built a new capital on the site of Gaur and established two cantonment towns near Dinajpur and Rangpur. He named his administrative divisions iqta and the governor of an iqta was designated as muqta. He built numerous mosques, madrasas and khanqahs. [ABM Shamsuddin Ahmed]