Lugal-Zage-Si (lugal-zag-ge4-si = LUGAL.ZAG.GI4.SI 𒈗𒍠𒄄𒋛; frequently spelled Lugalzaggesi, sometimes Lugalzagesi or "Lugal-Zaggisi") of Umma (reigned ca. 2296 - 2271 BC short chronology) was the last Sumerian king before the conquest of Sumer by Sargon of Akkad and the rise of the Akkadian Empire, and was considered as the only king of the third dynasty of Uruk. He was arguably the first king to unite Sumer as a single kingdom.
Lugal-Zage-Si pursued an expansive policy. He began his career as énsi of Umma, from where he conquered several of the Sumerian city-states - including Kish, where he overthrew Ur-Zababa; Lagash, where he overthrew Urukagina; Ur, Nippur, and Larsa; as well as Uruk, where he established his new capital. He ruled for 25 (or 34) years according to the Sumerian king list.
Lugal-Zage-Si claimed in his inscription that Enlil gave to him "all the lands between the upper and the lower seas", that is, between the Mediterranean Sea and the Persian Gulf. Although his incursion to the Mediterranean was, in the eyes of some modern scholars, not much more than "a successful raiding party", the inscription "marks the first time that a Sumerian prince claimed to have reached what was, for them, the western edge of the world". (Historical accounts from much later tablets asserted that Lugal-Anne-Mundu of Adab, a slightly earlier king, had also conquered as far as the Mediterranean and the Taurus mountains, but contemporary records for the entire period before Sargon are still far too sketchy to permit scholars to reconstruct actual events with great confidence.)
According to later Babylonian versions of Sargon's inscriptions, Sargon of Akkad captured Lugal-Zage-Si after destroying the walls of Uruk, and led him in a neck-stock to Enlil's temple in Nippur.