Prior to the discovery of his tomb, Tutankhamun was a shadowy figure from a chaotic period in Egyptian History, but a few tantalising clues in inscriptions pointed to his existance, and raised the possibility that there was a Royal burial, perhaps undiscovered for 4000 years, in the Valley of the Kings.
Although we know much about the goods that Tutankhamun took with him for the afterlife, information on his life is much less clear. Under his rule the 'Amarna' heresy was ended, and a transfer of power back to Thebes, and then priesthood there, was began.
Exactly how much of this would have been down to the 10 year old king is debatable, but we do have a fairly good idea of who the 'power behind the throne' would have been. Tutankhamun's successor as Pharaoh, Ay, and Ay's successor Horemheb were the real power in the country. Ay was one of the top advisors to the Amarna kings, and Horemheb enjoyed the status of head of the army.