Tyche (; Greek: Τύχη Ancient Greek: [tý.kʰɛː] Modern Greek: [ˈti.çi] "luck"; Roman equivalent: Fortuna) was the presiding tutelary deity who governed the fortune and prosperity of a city, its destiny. In Classical Greek mythology, she is the daughter of Aphrodite and Zeus or Hermes.
In literature, she might be given various genealogies, as a daughter of Hermes and Aphrodite, or considered as one of the Oceanids, daughters of Oceanus, and Tethys, or of Zeus. She was connected with Nemesis and Agathos Daimon ("good spirit").
The Greek historian Polybius believed that when no cause can be discovered to events such as floods, droughts, frosts, or even in politics, then the cause of these events may be fairly attributed to Tyche.
Increasingly during the Hellenistic period, cities venerated their own specific iconic version of Tyche, wearing a mural crown (a crown like the walls of the city). These are called the "Tyche of Alexandria" etc. This practice was continued in the iconography of Roman art, even into the Christian period, often as sets of the greatest cities of the empire. By then the Tyche were probably seen as merely personifications of the city with little religious significance.
Local Tyche had temples at Caesarea Maritima, Antioch, Alexandria, and Constantinople. In Alexandria the Tychaeon, the Greek temple of Tyche, was described by Libanius as one of the most magnificent of the entire Hellenistic world.
Stylianos Spyridacis  concisely expressed Tyche's appeal in a Hellenistic world of arbitrary violence and unmeaning reverses: "In the turbulent years of the Epigoni of Alexander, an awareness of the instability of human affairs led people to believe that Tyche, the blind mistress of Fortune, governed mankind with an inconstancy which explained the vicissitudes of the time."
Tyche appears on many coins of the Hellenistic period in the three centuries before the Christian era, especially from cities in the Aegean. Unpredictable turns of fortune drive the complicated plotlines of Hellenistic romances, such as, Leucippe and Clitophon or Daphnis and Chloe. She experienced a resurgence in another era of uneasy change, the final days of publicly sanctioned Paganism, between the late-fourth-century emperors Julian and Theodosius I, who definitively closed the temples. The effectiveness of her capricious power even achieved respectability in philosophical circles during that generation, although among poets it was a commonplace to revile her for a fickle harlot.
In late Roman sets the figures, usually four, represented the tyches of Rome, Constantinople, Alexandria, and either Antioch (more usual, as in the Esquiline Treasure of about 380 AD) or Trier, as in the Calendar of 354.
In Greco-Roman and medieval art she was depicted as carrying a cornucopia (horn of plenty), an emblematic gubernaculum (ship's rudder), and the wheel of fortune, or she may stand on the wheel, presiding over the entire circle of fate.