Hiero II, tyrant of Syracuse from 270 to 215 BC, was the illegitimate son of a Syracusan noble, Hierocles , who claimed descent from Gelo. He was an important figure of the First Punic War.

On the departure of Pyrrhus from Sicily (275 BC) the Syracusan army and citizens appointed him commander of the troops. He materially strengthened his position by marrying the daughter of Leptines, the leading citizen. In the meantime, the Mamertines, a body of Campanian mercenaries who had been employed by Agathocles, had seized the stronghold of Messana, whence they harassed the Syracusans. They were finally defeated in a pitched battle near Mylae by Hiero, who was only prevented from capturing Messana by Carthaginian interference. His grateful countrymen then made him tyrant (270).

In 264 BC he again returned to the attack, and the Mamertines called in the aid of Rome. Hiero at once joined the Punic leader Hanno, who had recently landed in Sicily; but being defeated by the consul Appius Claudius Caudex, he withdrew to Syracuse. Pressed by the Roman forces, in 263 he was compelled to conclude a treaty with Rome, by which he was to rule over the south-east of Sicily and the eastern coast as far as Tauromenium (Polybius i. 8-16; Zonaras Viii. 9).

From this time till his death in 215 BC he remained loyal to the Romans, and frequently assisted them with men and provisions during the Punic wars (Livy xxi. 49-51, xxii. 37, xxiii. 21). He kept up a powerful fleet for defensive purposes, and employed his famous kinsman Archimedes in the construction of those engines that, at a later date, played so important a part during the siege of Syracuse by the Romans.

A picture of the prosperity of Syracuse during his rule is given in the sixteenth idyll of Theocritus, his favourite poet. See Diod. Sic. xxii. 24-xxvi. 24; Polybius i. 8-vu. 7; Justin xxiii. 4.