Indo-Greeks contributed most to the Bhagavata cult.

Explanation:
The Bhagavata cult refers to the worship of Lord Vishnu, particularly in his form as Lord Krishna, as described in the Bhagavata Purana. This cult gained prominence during the post-Mauryan period in ancient India.

The Indo-Greeks were a Hellenistic kingdom that ruled over parts of northwestern India from the 2nd century BCE to the 1st century CE. They had a significant influence on the cultural and religious landscape of the region, including the development of the Bhagavata cult.

1. Spread of Bhagavata Cult:
- The Indo-Greeks played a crucial role in the spread of the Bhagavata cult through their patronage and promotion of Vaishnavism.
- They adopted and assimilated various aspects of Indian culture, including religious beliefs and practices.
- The Bhagavata cult, with its emphasis on devotion, love, and surrender to Lord Krishna, appealed to the Indo-Greeks and became popular among them.

2. Cultural Exchange:
- The Indo-Greeks facilitated a cultural exchange between Greek and Indian traditions, leading to the fusion of Greek and Indian religious ideas.
- The Greek concept of a divine hero, similar to the Indian idea of an avatar, merged with the worship of Lord Krishna in the Bhagavata cult.
- This syncretism resulted in the development of a unique religious tradition that incorporated elements from both Greek and Indian cultures.

3. Art and Architecture:
- The Indo-Greeks also influenced the art and architecture associated with the Bhagavata cult.
- They introduced Greek artistic styles and techniques, such as the use of realistic human figures and the depiction of narratives, into the creation of Bhagavata sculptures and paintings.
- These artistic representations further popularized the Bhagavata cult and made it accessible to a wider audience.

4. Historical Evidence:
- Historical evidence, such as coins and inscriptions, suggests that the Indo-Greeks actively patronized Vaishnavite temples and religious institutions.
- The presence of Greek inscriptions on Bhagavata sculptures and the depiction of Indo-Greek rulers offering prayers to Lord Krishna indicates their involvement in promoting the Bhagavata cult.

In conclusion, the Indo-Greeks played a significant role in the development and spread of the Bhagavata cult. Through their cultural exchange, patronage, and artistic contributions, they contributed to the popularity and acceptance of the Bhagavata cult in ancient India.