Ashoka the Great
Ashoka is often cited as one of India's greatest emperors. After a number of military conquests, he reigned over much of present-day India. He fought a war with the kingdom of Kalinga in which there was said to be 200,000+ casualties.
Afterwards, shaken by his brutal victory, he decided to become a Buddhist and lead with peace, not war. To do this, he set up hospitals for animals and humans, created shaded and rested areas along roads for weary travellers to rest, and dug wells in villages. We know these things about his life through various inscriptions (writing) on rocks and pillars. Asoka also convinced people to follow Buddhists paths.
The national emblem of India and the "Ashok Chakra" are created by Ashoka. It's in the flag to keep a remembrance of him.