Definitely the Maurya express! Named after the dynasty that first united the Indian sub-continent and laid the foundation to India as we know it today! The first name that comes up in any textbook or historical accounts of India's political history. Emperor Chandragupta Maurya unified and ruled the entire subcontinent (except TN, Kerala and the 7 sisters) including present day Pakistan, Balochistan and Bangladesh and his grandson Ashoka, is definitely the most famous ruler in Indian history!