Attributes of Krishna: Krishna - The Original Person

                                                                  Q. Recently I read this quote attributed to Srila Bhaktisiddhanta Saraswati Thakura purported to be published in the Harmonist (Sri Sajjana Tosani, Interview with Professor Johans, head of the Department of Philosophy, St. Xaviers College):

                                                                  Q. In Bg 3.22 purport, Srila Prabhupada writes "Although He (Lord Krishna) is above all the regulations of the revealed scriptures, He does not do anything that violates the revealed scriptures". And similarly in 2.23p: "because He descended to establish the principles of religion He followed the prescribed rules. Otherwise, common men would follow in His footsteps, because He is the greatest authority."

                                                                  Q. My question is regarding the Maha Mantra - HARE KRISHNA, HARE KRISHNA, KRISHNA, KRISHNA, HARE, HARE; HARE RAM, HARE RAM, RAM, RAM, HARE, HARE. Lords Krishna and Rama had different personalities and characters; both of them were avatara (incarnation) of Lord Vishnu in two different Yugas. My question is why these two names are combined in the Maha Mantra? Could you please kindly explain about the Maha Mantra? How did it derive? What are the meanings, if any, behind the Mantra?