The unification of Upper and Lower Egypt is traditionally attributed to King Narmer, also known as Menes, who ruled around 3100 BCE. Narmer is widely credited with defeating his enemies in Lower Egypt and uniting the two regions into a single kingdom, marking the beginning of the Early Dynastic Period of ancient Egypt

. Menes (possibly the same person as Narmer) is considered the first pharaoh to rule over both Upper and Lower Egypt, symbolizing the political and cultural unification of the country. He established Memphis as the capital city, strategically located between the two lands, and introduced centralized governance, religion, and economic development that laid the foundation for the Egyptian civilization

. The unification was symbolized by the Pschent, the double crown combining the white crown of Upper Egypt and the red crown of Lower Egypt, representing the pharaoh's dominion over both lands

. In summary:

• Upper and Lower Egypt were separate kingdoms along the Nile River.
• Around 3100 BCE, King Narmer (also called Menes) united them through military conquest and political consolidation.
• This unification established the first centralized Egyptian state and began the dynastic era.
• Memphis was founded as the capital city to govern the unified territory.
• The double crown symbolized the unity of the two lands under one ruler

Thus, King Narmer/Menes is the key historical figure credited with uniting Upper and Lower Egypt into one kingdom.