Vikramshila Mahavihara was established by the ruler of pala dynasty. Pala Dynasty was the ruling dynasty in Bihar and Bengal in India, from the 8th to the 12th century. Called the Palas because all their names ended in Pala, “protector”. The Palas rescued Bengal from the Chaos into which it had fallen after the death of Shashanka, a rival of Harsha of Kanauj. The founder of the dynasty was Gopala.

Vikramshila Mahavihara was established by the ruler of the Pala dynasty. Here is a detailed explanation of the answer:

1. Introduction:
- Vikramshila Mahavihara was a renowned Buddhist monastery or Mahavihara during the ancient period in India.
- It was located in present-day Bhagalpur district of Bihar, India.
- The establishment of Vikramshila Mahavihara played a significant role in promoting Buddhism and providing education to Buddhist scholars.

2. Background on the Pala dynasty:
- The Pala dynasty was a prominent imperial dynasty that ruled over the Indian subcontinent from the 8th to the 12th century.
- They were staunch supporters of Buddhism and actively promoted its growth.
- The Pala dynasty had its capital at Pataliputra (modern-day Patna).

3. Establishment of Vikramshila Mahavihara:
- Vikramshila Mahavihara was established around the late 8th or early 9th century by King Dharmapala of the Pala dynasty.
- King Dharmapala was a devout Buddhist and wanted to establish a center of learning and spiritual practice for Buddhist scholars.
- Vikramshila Mahavihara was strategically located near the Ganges River, which facilitated trade and communication.

4. Significance of Vikramshila Mahavihara:
- Vikramshila Mahavihara became one of the most important centers of Buddhist learning in ancient India.
- It attracted scholars from various parts of the world, including Tibet, China, and Southeast Asia.
- The Mahavihara offered a comprehensive curriculum that included the study of various Buddhist texts, philosophy, logic, grammar, and other subjects.
- It served as a platform for intellectual debates and discussions, contributing to the development and dissemination of Buddhist thought.

5. Decline and revival:
- Vikramshila Mahavihara experienced a gradual decline after the decline of the Pala dynasty in the 12th century.
- It was eventually abandoned and fell into ruins.
- However, in recent years, efforts have been made to revive the glory of Vikramshila Mahavihara as a center of Buddhist studies and research.

In conclusion, Vikramshila Mahavihara was established by the ruler of the Pala dynasty, King Dharmapala. It played a crucial role in promoting Buddhism and providing education to Buddhist scholars. The Pala dynasty's support for Buddhism and their patronage of institutions like Vikramshila Mahavihara contributed to the growth and spread of Buddhism in ancient India.