Tyche

Tyche (Τύχη in Ancient Greek) is the goddess of luck and prosperity, whose Roman counterpart is Fortuna.

History
The daughter of Oceanus and Tethys, Tyche is one of the three thousand Oceanids. In ancient times, Tyche was worshiped as the deity who presided over city and individual prosperity. She is the opposite of her sister Nemesis who is the goddess of balance.

Fortuna
Tyche can change into her Roman counterpart of Fortuna. As Fortuna, she becomes more disciplined, militaristic, and warlike. She may have children or descendants at Camp Jupiter near San Francisco. The Greeks envisioned Tyche as a beneficiary and unpredictable being. The Romans honored Fortuna each year with a celebration called the Festival of Fortuna, which is continued by the campers of Camp Jupiter.

Trivia

 * Tyche's cabin at Camp Half-Blood is Cabin 19.
 * According to Rick Riordan's website, Tyche is the most difficult Goddess to find. It is said that if you just keep on praying for good luck, she's not as likely to give you some, and that if you just go ahead and do something, chances are she may lend you some. This explains the generally random behavior of her children.
 * Sometimes the Constellation Virgo is associated with her.
 * On Rick Riordan's website, Nemesis is said to be sisters with her Roman counterpart, Fortuna. Whether this is true to the series or if Rick Riordan made a mistake is unknown.
 * Sometimes she is seen as a Titan rather than a God.