Tutankhamun ascended the throne at the age of 9 yrs and ruled until his death, ten yrs later, at the age of 19. His throne name was Neb-Kheperu-Re, which means "Lord of Manifestations is Re".

Prior to Howard Carter's discovery of his tomb, almost nothing was known of him and interestingly, the one disappointment in Carter's discovery was that there was little documentation found within his tomb.

Therefore, we still know relatively little about Tutankhamon. Yet, Tutankhamon is, in modern times, the most famous of the Pharaohs, and the only one to have a nickname in popular culture ("King Tut").

Life:

Tutankamun was not given this name at birth, but rather Tutankhaten (meaning "Living Image of the Aten), squarely placing him in the line of pharaohs following Akhenaten, the heretic pharaoh, who was most likely his father. He changed his name in year two of his rule to Tutankhamun (which means "Living Image of Amon, which is actually a reference to Karnak).

When he became king, he married his half sister, Ankhesenepatan, who later changed her name to Ankhesenamun. They had two daughters, both stillborn - their mummies were discovered in his tomb.

King Tut was the result of an incestuous relationship and, because of that, may have suffered from several genetic defects that contributed to his early death. His mother was one of Akhenaten's five sisters, although it is not known which one. His congenital flaws are more common among the children of incest.

Reign:

Given his age, the king must have had very powerful advisers, presumably including General Horemheb, the Vizier Ay, and Maya the "Overseer of the Treasury". Horemheb records that the king appointed him Lord of the Land as Hereditary Prince to maintain law.

In his third reignal year, Tutankhamun reversed several changes made during his father's reign. A move was made, probably under the direction of Ay and Horemheb, to return Egypt to its traditional ancient religion.

He ended the worship of the god Aten and restored the god Amun to supremacy. The ban on the cult of Amun was lifted and traditional privileges were restored to its priesthood.

His building work at Luxor included the continuation of the entrance colonnades of the Amenhotep III temple, including associated statues. As part of his restoration, the king initiated building projects, in particular at Thebes and Karnak, where he dedicated a temple to Amun, embellished with images of Amun, Amunet and Khonsu.

We also know, mostly from fragments, that he built at Memphis. At Kawa, in the far south, he built a temple. Pair of granite lions from that temple flanks the entrance to the Egyptian Sculpture Gallery at the British Museum.

Military wise, little happened during the reign of Tutankhamun. The country was economically weak and in turmoil following the reign of Akhenaten. Diplomatic relations with other kingdoms had been neglected, and Tutankhamun sought to restore them, in particular with the Mitanni. Evidence of his success is suggested by the gifts from various countries found in his tomb.

Despite his efforts for improved relations, battles with Nubians and Asiatics were recorded in his mortuary temple at Thebes. There are paintings in the tomb of Horemheb and as well as the tomb of Huy that seem to confirm these campaigns, though it is unlikely that the young Tutankhamun actually took part in the military actions directly.

The campaigns in Palestine/Syria met with little success, but those in Nubia appear to have gone much better.
Death:

Although there is some speculation that Tutankhamun was assassinated, the general consensus is that his death was accidental. CT scan taken in 2005 shows that he had badly broken his leg shortly before his death, and that the leg had become infected. He was infected with the most severe strain of malaria several times in his short life. It is believed that these two conditions combined led to his death.