The word "pharaoh" comes from the Bible. It was first used by Joseph and Moses in the "Second Book of Kings" (ch.17). Although we use this word without distinction, it is an anachronism when used to refer to the Egyptian kings prior to the eighteenth dynasty.
The pharaohs began ruling Egypt in 3000 B.C., when Upper and Lower Egypt were united. During the Old Kingdom (2575-2134 B.C.), they considered themselves to be living gods who ruled with absolute power. They built pyramids as testimony of their greatness but left no official records of their achievements.
By the Middle Kingdom, the pharaohs no longer considered themselves to be living gods, but rather the representatives of the gods on earth. They left records of their deeds, but these were no more than a string of titles and laudatory epithets.
To reinforce their image as powerful divine rulers, the pharaohs represented themselves in writings and sculptured reliefs on temple walls. They often depicted themselves as warriors who single-handedly killed scores of enemies and slaughtered a whole pride of lions. Similar depictions were repeated by one pharaoh after another, which leads one to question the validity of the scenes. For example, the war pictures of Rameses III at Karnak are exact copies of those of Rameses II. These deeds of heroism were, in part, designed for propaganda purposes. They reinforced the position of the king as head of state rather than reflecting historical reality.
In the fourth century B.C., a high priest and scribe of the sacred shrines of Egypt named Manetho compiled the first comprehensive list of the pharaohs. He grouped their reigns into dynastic divisions that to a large degree are still considered accurate today. The dynasties are grouped into several periods, starting with the Early Period (3000-2575 B.C.) and ending with the Graeco-Roman Period (332 B.C.- A.D. 395). The first dynasty began with the legendary King Menes (who is believed to have been King Narmer), and the last one ended in 343 B.C. when Egypt fell to the Persians. Nectanebo II was the last Egyptian-born pharaoh to rule the country.
Not all the pharaohs were men, nor were they all Egyptian. Before the Graeco-Roman Period, at least three women ascended the throne, the most important being Queen Hatshepsut. Over several periods, Egypt was dominated by foreign powers that appointed a king from their own ranks. Exactly how successive pharaohs were chosen is not entirely clear. Sometimes a son of the pharaoh, or a powerful vizier (head priest) or feudal lord assumed the leadership, or an entirely new line of pharaohs arose following the collapse of the former monarchy.