Seleucus Nicator was defeated by option 2, Chandragupta Maurya. Chandragupta Maurya was the founder of the Mauryan Empire in ancient India. He successfully established a vast empire that stretched from present-day Afghanistan to Bangladesh. In order to expand his empire, Chandragupta waged wars against various regional rulers, including Seleucus Nicator, who was a general under Alexander the Great.

The defeat of Seleucus Nicator by Chandragupta Maurya is historically significant because it marked the first time that a ruler from the Indian subcontinent had defeated a powerful foreign adversary. This victory further solidified Chandragupta`s empire and allowed him to establish strong diplomatic relations with other major powers of the time.

Overall, the defeat of Seleucus Nicator by Chandragupta Maurya played a crucial role in shaping the political landscape of ancient India and establishing the prominence of the Mauryan Empire.