Sargon of Akkad, The first king
When looking at human history as a whole, kings and emperors have always been present. There is, however, always a first to everything. That's not to say that someone 'invented the concept of a king. Many probably came up with this idea without knowing others did as well. It is also hard to know exactly what happened that far back in time.
However, we can trace it back to the person who is still considered the first true king in human history. His name is Sargon of Akkad, founder of the Akkadian Empire (also believed to be the first empire). Even if the Sumerian civilization predated the Akkadian Empire, they were more like independent cities (like Ur, Uruk and Kish) rather than a unified nation.
Sargon is the man who laid down the duties of a leader beyond military might. Concepts like a common language, global trades and central taxations were created under his reign. He also taught his son, Rimush, how to lead an empire – instigating the concept of a dynasty. Sargon was so successful that his family stayed in power over many generations, going as far as his grandson, Naram-Sin. This may not sound like much, but you have to know that the same generations could hold many monarchs, as Rimush was succeeded by one of his brothers. Sargon's legacy would live on until our days, as his work inspired many others to rise to power, and even today, many of his principles are still used by modern governments.