Nabuna'eed (Neo-Babylonian Akkadian: 𒀭𒀝𒈾𒀪𒀉, romanized: Nabû-naʾid, Hellenized as Nabonidus meaning "May Nabu be exalted" or "Nabu is praised") was the last king of the Neo-Babylonian Empire, ruling from 556 BC to the fall of Babylon to the Achaemenian Empire under Cyrus the Great in 539 BC. Nabonidus was the last native ruler of ancient Mesopotamia, the end of his reign marking the end of thousands of years of Sumero-Akkadian states, kingdoms and empires. He was also the last independent king of Babylon. Regarded as one of the most vibrant and individualistic rulers of his time, Nabonidus is characterised by some scholars as an unorthodox religious reformer and as the first archaeologist.
The origins of Nabonidus, his connection to previous royalty, and subsequently what claim he had to the throne remain unclear, given that Nabonidus made no genealogical claims of kinship to previous kings. This suggests that he was neither related nor connected to the Chaldean dynasty of Babylonian rulers. However, he is known to have had a prominent career of some kind before he became king. It is possible that he was connected to the Chaldean kings via marriage, possibly having married a daughter of Nebuchadnezzar II (r. 605–562 BC). Nabonidus's mother, Adad-guppi, was of Assyrian ancestry. His father, Nabu-balatsu-iqbi, of whom little is known, may also have been either Assyrian or Babylonian. Some historians have speculated that either Adad-guppi or Nabu-balatsu-iqbi were members of the Sargonid dynasty, rulers of the Neo-Assyrian Empire until its fall in 609 BC.