Cythonna is the Kryptonian Goddess of Ice and Darkness and is Rao's opposite counterpart. Rao imprisoned her many eons ago, and she's held a terrible grudge against him ever since the imprisonment. Eons later, she escaped and made her way to Earth, where she battled Superman.
Cythonna was created by Walt Simonson, Greg Hildebrandt, and Tim Hildebrandt, first appearing in Superman: The Last God of Krypton. (1999)