Final answer:
Sargon of Akkad was the influential Akkadian king who established the first known empire in history around 2340 BCE, profoundly changing the political landscape of Mesopotamia.
Step-by-step explanation:
The Akkadian king who reshaped the political landscape of Mesopotamia during the 3rd millennium BCE was Sargon of Akkad. Around 2340 BCE, Sargon established the Akkadian Empire, effectively ending the era of independent Sumerian city-states. This empire was the first known to history and set the foundation for future empires in the Near East. Under Sargon's rule, the Akkadian Empire controlled a vast region and utilized an administrative system that influenced subsequent dynasties and empires such as the Third Dynasty of Ur, the Babylonian kingdom under Hammurabi, and later the Assyrian and Neo-Babylonian empires.
Sargon's legacy was such that his empire became a model for imperial expansion and governance. The political, administrative, and military systems established by Sargon were adopted by later rulers, significantly impacting the structure of Near Eastern civilizations for centuries to come. The introduction of the world's first standing army and the unification of Akkad and Sumer were among his notable achievements.