The ancient Egyptians had always worshiped the Aten (the Sun God), as one of the many gods in their pantheon.
But towards the end of the 18th dynasty, in about 1351 BC, a Pharoah, Akenaten, decided that the Aten was the one true god and tried to force the Egyptian people to worship the god exclusively. He was actually born Amenhotep IV, son of Amenhotep III, a very successful pharaoh, but he changed his name to Akenaten which meant "of great use to Aten". As an absolute ruler, he had some superficial success in changing the religion - while he was alive.
Five years after he ascended to the throne, Akenaten decided to build a new city in worship of the Aten. The entire court was moved to a place in the middle of a desert and lived in camps as the new city Armana was constructed. A fortune was spent creating this new city - something that worried Egyptians as the national treasury began to deplete. Akenaten also started to close the temples to the other gods (Amun, Ra, Osiris etc) across Egypt. He insisted that the Egyptians all worship the one true god, the Aten.
This had profound implications:
The polytheism of the ancient Egyptians encouraged a world view where peace and balance were emphasized and religious tolerance was not considered an issue; there is not even a word directly corresponding to the concept of `religious tolerance' in the ancient Egyptian texts. A hallmark of any monotheistic belief system, however, is that it encourages the belief that, in order for it to be right, other systems must necessarily be wrong. This insistence on being the sole arbiter of ultimate truth leads to intolerance of other beliefs and their suppression; this is precisely what happened in Egypt.
In year 9 of his reign, Akenaten banned images of the other gods, and images of the Aten itself were reduced to a simple sun disc.
As time went by, Akenaten began to believe that he was the son of the Aten (we know this from inscriptions in Armana which called him the son of Aten) - traditional processions of chariots carrying images of the gods on feast days were replaced with Akenaten and his wife Nefertiti on chariots making the procession - with the clear implication that they were the gods.
This also disturbed the Egyptians. Traditionally the Pharaoh interceded with the gods on their behalf, but none had claimed they were gods themselves or sons of god.
The closing of the temples of Amun in particular had a profound effect on the economy. By the 18th dynasty, Ancient Egyptian civilisation was two thousand years old, and it's success in creating a stable, calm state in the middle of the desert lay in it's ability to feed all it's people and have a surplus on top to pay for luxuries.
Egypt was fed all year on a single harvest which depended on the annual flooding of the Nile. The priests of Amun acted as ancient scientists, carefully measuring the rising of Nile's waters, so they could give the signal as to the best time to sow the crops. When the signal was given, Egyptians rushed to plant the crop, and the priests then co-ordinated all farming activity right up to the harvest. They also collected and distributed the grain to all corners of Egypt, so that every one was fed.
When Akenaten destroyed this system, famines started to appear. And the weakened population was subject to various epidemics.
Akenaten appears to have blamed the famines on the population for not worshiping the Aten properly and sought to crack down even harder.
On his death, his nine year old son, Tutenkaten succeeded him. His advisors renamed him Tutenkamun and moved the court back to Thebes where the old religion (and economy) revived.
All traces of Akenaten were obliterated, he wasn't even mentioned on the list of kings the Egyptians like to make. In fact, until the 20th century, when Armana was rediscovered in the desert, the existence of Akenaten had been obliterated for 3000 years. We only know his story because Armana itself was full of walls with text telling Akenaten's story. Egyptian aversion to Akenaten was so great that no-one had lived in Armana since Akenaten died, not even a few stray villagers.
Birth of Monotheism
He did have a legacy though. The Bible tells the story of Moses who is an Egyptian boy, discovered as a baby in a rush basket by the Pharoah's daughter and raised with the Pharoah's family.
The interesting thing about this story is that this is an old Egyptian myth predating the Bible by several thousand years. The god Horus is produced by the goddess Isis (the water goddess) and left in a rush basket for Nephthys (the sister of Isis) to find and raise.
The name Moses is also interesting. Sigmund Freud was convinced it derived from the Ancient Egyptian word "mose" which meant child.
The twist on Moses story is that he is found by the Pharoah's daughter. But which Pharoah? If it was Akenaten, then the young Moses would have been raised in the cult of the Aten, the one true god.
At the death of Akenaten, when Atenism was obliterated, those few people who still worshiped the Aten as the one true god would have been relegated to the fringes of society and regarded with suspicion because of their association with Akenaten.
From Moses we get the beginning of Judaism, the idea of the one true god, the jealous god who punishes those who don't worship him properly or those who worship others. And the idea that there could be a son of this one true god, the messiah. And also the idea that Jews are always on the fringes, regarded with suspicion.
We have one more connection between Judaism and Atenism: When excavating Armana, one of the tombs had a prayer in hieroglyphics inscribed on it. It was the Great Hymn to the Aten, which we know of as Psalm 104, which appeared in the Bible a thousand years later, which in turn was recording what was then an old prayer.
Moses led his band of monotheists out of Egypt to settle in the Kingdom of Canaan, which already spoke Hebrew, and they likely settled there and adopted Hebrew and other Canaanite/Semitic practices. But their origins were Egyptian and their religion lay in a religious revelation a long forgotten Pharoah had had.