(Τύχη Ἀγαθή), commonly referred to as simply Tyche, was a Greek guardian spirit
who watched over cities. Although she was technically a protector, she was also blamed for anything bad that happened to a city, and thus was sometimes vilified or feared in stories and poems. During the Hellenistic
period Tyche clearly split from being one entity into many personifications, one for each major city; thus you might hear of Tyche of Antioch
or Tyche Protogeneia
Tyche appeared human in appearance, as a young woman with no apparent godly aspect. She was usually represented as wearing a mural crown -- that is, a crown designed to look like the walls of a city. In later representations she came to be depicted as carrying a cornucopia, a ship's rudder, and the wheel of fortune.
She is given various life stories by various writers; she is most often said to be the daughter of either Hermes and Aphrodite or of Zeus and Aphrodite. However, some stories had her as one of the Oceanids, the daughters of Oceanus and Tethys. She was the companion of Agathos Daimon, the protector of rural areas. As Nemesis slowly became perceived as a punishing goddess, Tyche came to be seen as her counterpart, the positive force counteracting Nemesis' (admittedly just) punishing force.
Pronounced /ˈtaɪki/, Tyche comes from the Greek Τύχη meaning 'luck'; 'Tyche Agathe' literally meant 'good luck', or 'good fortune'. She later became the basis for the Roman Fortuna.
Astronomically, Tyche is used for three different things. First, the constellation of Virgo has sometimes been identified as Tyche, although it is more common to identify it as Astreaea, or, sometimes, Demeter. Second, Tyche is the name given to a hypothetical gas giant located in the Oort cloud, which astronomer John Matese proposed to explain the movement of long-period comets. And finally, 258 Tyche is one of the larger asteroids in our asteroid belt.