They were rulers who united lands under one rule.
Sargon II was king of Assyria, reigning from 722 to 705 BC. In 710 BC, Sargon II successfully conquered the nearby rival kingdom of Babylon. So Assyria and Babylon were the main lands he united under one rule (in addition to other conquests).
Darius I, who ruled over the empire of Persia from 522–486 BC, united the kindgoms of the Medes and the Persians.
Chandragupta Maurya reigned over the Maurya Empire in ancient India from 321–297 BC. He conquered the Nanda Empire and eastern provinces of the Seleucid Empire, thus uniting several lands under one rule.
Shihuangdi was the “First Sovereign Emperor” (that was the meaning of his title Shihunagdi) who established the Qin dynasty and the first unified Chinese empire. He ruled from 221-210 BC.
