Born in 326 BC in Samothrace (present day Greece), Katherine was a foundling child. Raised by a loving family who taught her how to help others, she helped heal people with her knowledge of remedies, later becoming a healer for others as she grew older. In 292 BC, a volcanic eruption caused the death of many in her village, claiming her life as well. Following her first death and later revival, she met her teacher, Mantinea of Pylus, who taught her what she was, and how to survive.

Katherine's weapon of choice was a German hand-and-a-half sword. In this, she is quite different from most female Immortals who tended to gravitate toward lighter, smaller blades. But despite experiments with other style blades, she consistently favored the sturdy versatility of the hand-and-a-half.