Theory:

Dharmapala (A.D. 770 - 810)
 
Gopala laid the foundations of the Pala dynasty in Bengal. A group of regional chieftains elected him as he did not have royal antecedents. Gopala’s son, Dharmapala, was the real founder of the Pala Dynasty because he greatly expanded the boundaries of the empire. He was an ardent follower of Buddhism. Vikramashila Monastery, the great center of Buddhist learning, was founded by Dharmapala.
 
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The ruins of, ancient university of India:
Vikramshila University

Dharmapala was followed by his son, Devapala. He expanded the extent of the Pala Empire by conquering Kamarupa (present-day Assam). Devapala was a firm Buddhist and constructed many temples and monasteries in Magadha. Also, he gifted five villages to Buddhists.
Ramacharita was written during the rule of Devapala. In which, Pala rulers were acclaimed as the descended of Solar Dynasty.
Mahipala I (988 - 1038)

Mahipala I was acclaimed as the founder of the second Pala dynasty, as he expanded the boundaries of the Pala dynasty to Varanasi. Palas took a preeminent role in north India after the decline of the Pratiharas. But he could not extend his domain to the south due to intense campaigns of the Chola king, Rajendra Chola. Mahipala, as the restoration of the old glory, constructed and repaired many religious buildings at Banaras, Sarnath and Nalanda.
 
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Ancient Buddhist monasteries
near Dhamekh Stupa, Sarnath.
 
The Pala dynasty declined after the death of Mahipala. Ramapala was the last strong Pala ruler. The kingdom was divided during his son Kumarapala’s rule. After that, the Sena dynasty replaced the Palas.
Dhamek Stupa, located in Sarnath, is a solid cylinder of bricks and stones, 128 feet high and more than 90 feet in diameter, completed in the year 500A.D. The site is important to Buddhism.