Ratha means a chariot . Rathi means a chariot-mounted fighter . Ancient Indian military had 4 wings(=anga's); chariots,elephants,horse and foot soldiers. Hence the name chathuranga (4 wings) to a fullfledged army which name was given to the famous game chess, wherein 4 types of pieces are used too.
In days of Mahaabhaaratha, Arjuna was considered to be the best archer and the most valorous chariot-man.
In the great war of Mahaabhaaratham, Krishna was Arjuna's charioteer. Krishna was Arjuna's cousin and brother-in-law too.
He vowed that he wouldn't fight in the war himself but promised victory.
As promised, Krishna guided the Paandavas to victory against the mighty Kouravas through many a way, plauded and derided. The combination of the two ran terror among the enemies playing such a havoc that even Karna, no less than Arjuna, could not guard Kouravas despite his best efforts.
Krishna and Arjuna were more remembered for the outcome of The Geetha
than their valour.
It was when Arjuna felt disgusted in the starting moment of the war for having had to kill his kin and kith simply for the sake of
kingdom, that Krishna taught him the philosophy of life to enlighten the truth about the bonds,life,death and birth. This famous discourse is nothing other than the esteemed Bhagavadgeetha.
Krishna was a true symbol of driving force and Arjuna that of a true agent.