Tyche (Luck)

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, and at this time served to bring  positive messages to people, relating to external events outside their control.  During the Hellenistic period, with dramatic socio-political changes starting  with Alexander the Great, Tyche increasingly embodied the whims of fate (both  negative and positive), eclipsing the role of the Olympic gods. 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.

Source  Wikipedia