When Tutankhaten came to the throne, there was a religious and political crisis in Egypt. Ay, the Pharaoh's guardian, used Tutankhaten's youth to get back the power and establish the original religion again. Tutankhaten accepted the name Tutankhamun and his wife Ankhesenpaaten also accepted a new name - Ankhesenamun. Tutankhamun was reconciled with the priesthood then and declared a return to original Gods and abolished festivals. Thebes (Waset) became the capital again.
Tutankhamun ruled approximately for 10 years (1,347 - 1,338 BC) and he died at age of twenty. After his death Ay married his wife and he ruled for the next 4 years. Then general Horemheb was put on the throne by the priesthood, who is considered as a factual founder of the 19th dynasty - the Ramesses dynasty.
Tutankhamun's death was unexpected - he was only 20 after all. Tutankhamun's tomb KV 62 was far from finishing, so there was a need to choose an alternative grave quickly. In the end a rather modest tomb was chosen likely intended for Ay. The craftsmen had 70 days for finishing the Tutankhamun's tomb. You can read about the death of Tutankhamun on another site of this web.
Tutankhamun would stayed unknown without an archaeologist Howard Carter, who discovered his tomb KV 62 in the Valley of the Kings. We haven't known whose son Tutankhamun was for a long time - if he was a son of Amenhotep III or maybe Ay - a high priest of Amun's cult. A DNA research of Tutankhamun's, Akhenaten's, Tiye's and two other unknown mummies was made only recently, which found out that Amenhotep IV (Akhenaten) was the father of Tutankhamun and his mother was one of Akhenaten's sisters (her name hasn't been determined yet definitively).