Sargon II (Neo-Assyrian Akkadian: 𒈗𒁺, romanized: Šarru-kīn, meaning "the faithful king" or "the legitimate king") was the king of the Neo-Assyrian Empire from 722 BC to his death in battle in 705. Probably the son of Tiglath-Pileser III (r. 745–727), Sargon is generally believed to have become king after overthrowing Shalmaneser V (r. 727–722), probably his brother. He is typically considered the founder of a new dynastic line, the Sargonid dynasty.

Modelling his reign on the legends of the ancient rulers Sargon of Akkad, from whom Sargon II likely took his regnal name, and Gilgamesh, Sargon aspired to conquer the known world, initiate a golden age and a new world order, and be remembered and revered by future generations. Over the course of his seventeen-year reign, Sargon substantially expanded Assyrian territory and enacted important political and military reforms. An accomplished warrior-king and military strategist, Sargon personally led his troops into battle. By the end of his reign, all of his major enemies and rivals had been either defeated or pacified. Among Sargon's greatest accomplishments were the stabilization of Assyrian control over the Levant, the weakening of the northern kingdom of Urartu, and the reconquest of Babylonia. From 717 to 707, Sargon constructed a new Assyrian capital named after himself, Dur-Sharrukin ('Fort Sargon'), which he made his official residence in 706.

Sargon considered himself to have been divinely mandated to maintain and ensure justice. Like other Assyrian kings, Sargon at times enacted brutal punishments against his enemies but there are no known cases of atrocities against civilians from his reign. He worked to assimilate and integrate conquered foreign peoples into the empire and extended the same rights and obligations to them as native Assyrians. He forgave defeated enemies on several occasions and maintained good relations with foreign kings and with the ruling classes of the lands he conquered. Sargon also increased the influence and status of both women and scribes at the royal court.

Sargon embarked on his final campaign, against Tabal in Anatolia, in 705. He was killed in battle and the Assyrian army was unable to retrieve his body, preventing a traditional burial. According to ancient Mesopotamian religion, he was cursed to remain a restless ghost for eternity. Sargon's fate was a major psychological blow for the Assyrians and damaged his legacy. Sargon's son Sennacherib was deeply disturbed by his father's death and believed that he must have committed some grave sin. As a result, Sennacherib distanced himself from Sargon. Sargon was barely mentioned in later ancient literature and nearly completely forgotten until the ruins of Dur-Sharrukin were discovered in the 19th century. He was not fully accepted in Assyriology as a real king until the 1860s. Due to his conquests and reforms, Sargon is today considered one of the most important Assyrian kings.

Nothing is known of Sargon II's life before he became king. He was probably born c. 770 BC and cannot have been born later than c. 760 BC. His reign was immediately preceded by those of Tiglath-Pileser III (r. 745–727) and Tiglath-Pileser's son Shalmaneser V (r. 727–722). Although Sargon is generally regarded as the founder of a new dynastic line, the Sargonid dynasty, he was probably a scion of the incumbent Adaside dynasty. Sargon grew up during the reigns of Ashur-dan III (r. 773–755) and Ashur-nirari V (r. 755–745), when rebellion and plague affected the Neo-Assyrian Empire; the prestige and power of Assyria dramatically declined. This trend reversed during the tenure of Tiglath-Pileser, who reduced the influence of powerful officials, reformed the army and more than doubled the size of the empire. In contrast to Tiglath-Pileser, little is recorded of Shalmaneser's brief reign.

Whereas kings typically elaborated on their origin in inscriptions, Sargon stated that the Assyrian national deity Ashur had called him to the throne. Sargon mentioned his origin in just two known inscriptions, where he referred to himself as Tiglath-Pileser's son, and in the Borowski Stele, probably from Hama in Syria, which referenced his "royal fathers". Most historians cautiously accept that Sargon was Tiglath-Pileser's son but not the legitimate heir to the throne as the next-in-line after Shalmaneser. If Sargon was Tiglath-Pileser's son, his mother might have been the queen Iaba. Some Assyriologists, such as Natalie Naomi May, have suggested that Sargon was a member of a collateral branch of the Adaside dynasty from the western part of the empire. In Babylonia, Sargon and his successors were considered part of the "dynasty of Hanigalbat" (a western territory), while earlier Assyrian kings were considered part of the "dynasty of Baltil" (Baltil being the name of the oldest portion of the ancient Assyrian capital of Assur). Perhaps Sargon was connected to a junior branch of the royal dynasty established at Hanigalbat centuries earlier. Some Assyriologists, such as John Anthony Brinkman, believe that Sargon did not belong to the direct dynastic lineage.

The Babylonian Chronicles report that Shalmaneser died in January 722 and was succeeded in the same month by Sargon, who was between forty and fifty years old. The exact events surrounding his accession are not clear. Some historians such as Josette Elayi believe that Sargon legitimately inherited the throne. Most scholars however believe him to have been a usurper; one theory is that Sargon killed Shalmaneser and seized the throne in a palace coup. Sargon rarely referenced his predecessors and, upon accession, faced massive domestic opposition. Shalmaneser probably had sons of his own who could have inherited the throne, such as the palace official Ashur-dain-aplu, who retained a prominent position under the Sargonid kings. Sargon's only known reference to Shalmaneser describes Ashur punishing him for his policies:

Shalmaneser, who did not fear the king of the world, whose hands have brought sacrilege in this city (Assur), pu[t on...] on his people, [he] impo[sed] the compulsory work and a heavy corvée, paid them like a working class [...]. The Illil of the gods, in the wrath of his heart, overthrew [hi]s rule, and [appointed] me, Sargon, as king [of Assyria]. He raised my head; he let [me] take hold of the scepter, the throne (and) the tiara [...].