Amenhotep IV. came to the throne around 1,375 BC, when he was sixteen. He became the Pharaoh, because his elder brother Thutmose died. Powerful church ruled the Egypt then, which was supported by Amenhotep's father. Large property were concentrated in the church's temples sacred to Amun.
Childhood Amenhotep IV. (Akhenaten)
Future Akhenaten didn't have an easy childhood - the father didn't love him much, but the more favourite he was to his mother Tiye. He rather observed the sky instead of improving in fencing and other things, which were more suitable for a young prince. We know that he suffered from epilepsy since he was a child, so his mother took special care of him and pamper him.
Beginning of religious reform
Young Amenhotep IV. tried to restrict the power of priests of the Amun's temple in Karnak after his wedding with beautiful princess Nefertiti (she probably was a princess of Asian origin) but he wasn't successful. Maybe this was his reason for reviving the cult of Aten (whatever influence was it - her young wife Nefertiti or mysticism he was attracted to since his childhood) - a god of ancient city Heliopolis.
Amenhotep IV. realized that the power of church could be disrupted only with a radical change. In the sixth year of his rule he decided that the only Got of Egypt would be Aten and he prohibited all other deities worshipped for thousands years! He let close all Amun's temples and the name of prohibited God had to be destroyed in all Egypt. The Pharaoh himself changed the name to Akhenaten ("Useful for Aten") and also a cartouche with this name was discovered. This reform was accompanied with brutal repressions.
Akhetaten - a new capital
Amenhotep IV. - then Akhenaten - left the capital Thebes (Waset) and founded a new capital Akhetaten (present name is el-Amarna) further downstream the Nile. It was situated midway between Thebes (Waset) and Mennefer. The city was built on a boundary between the desert and about 12 km long zone of fertile land in short time. And on the top of that the Pharaoh chnged his name from Amenhotep IV to Akhenaten (useful for Aten).
Catastrophic foreign affairs
Akhenaten closed himself in the new capital, didn't perceived the world around him and didn't even realize that his kingdom gradually declined. In contraty to his predecessors Akhenaten refused to send gold and other presents to the allies for support of diplomatic relationships. His closest surroundings were made by thoughtless scribes and administrators, who cared only for their own enrichment. Some of them even sold out to the Hittites. The borders weren't guarded so well as in times of Akhenaten's predecessors rule.
The situace on the east was alarming. The Hittites were encouraged by the Pharaoh's inactivity and they were bigger and bigger threat. The Kingdom of Mitanni couldn't fight off the Hittite soldiery that attacked its territory. Only after the Hittites gained the Kingdom of Mitanni definitively, the Pharaoh decided to find allies in raging country as his advisors told him. He presumed that he found an ally in an Amorite ruler Abdi-Ashirta, but he and also his son Aziru ran a doubtful politics - they alternately were inclined to the Pharaoh or the Hittites. So the Egyptian Empire "shrank" only into an area around the Nile in ten years.
The Pharaoh fell out with Nefertiti in the end of his reign - probably because of religious divergences. Akhenaten apparently wanted to become reconciled to Amun's clergy and so he ruled together with certain Smenkhkare then. But there is no much information about him (according to one theory he might be one of his brothers). One sure thing is that Akhetaten let Smenkhkare marry his daughter Meritaten.
We don't know how Akhenaten died. His wife was raising the future ruler Tutankhaten (he changed his name to Tutankhamun after the cult of Amun was established again), who became famous around the world - unfortunately it was not until his death and thanks to the discovery of his tomb in the twentieth of 20th century.