Who was the first king of India?

The first king of a united India is considered to be Chandragupta Maurya, who founded the Maurya Empire. Before Chandragupta, India had many regional rulers, janapadas, and mahajanapadas. 

He was the first to bring most of the Indian subcontinent under one empire. While “first king of India” can be debated because earlier kingdoms existed, Chandragupta Maurya is widely accepted in history as the first pan-Indian emperor.