Katerina Petrova (Cyrillic: Катерина Петрова) was born into a noble and wealthy Bulgarian family on June 5, 1473. In 1490, when she was about 16 or 17 years of age, Katerina became pregnant by an unknown man, a Traveler, and her family disowned her for the shameful birth of a daughter. She carried the child to term, but seconds after her daughter's birth, Katerina's father took the child away and gave the child to another family, and didn't even Katherine hold her baby once. Katerina was devastated by this and was banished to England, where she admitted to "quickly becoming English." In 1492, she met Trevor, who introduced her to Lord Elijah, who in turn introduced her to his younger brother, Lord Niklaus. Katerina was attracted to Klaus until she found out what he was, and that he was planning on using her as a sacrifice to break the Hybrid Curse placed on him. She escaped with the help of Trevor, who had fallen in love with her. He led her pursuers astray and told her to go east to a cottage in the woods where she would be safe. When she arrived at the cottage, Katerina met a vampire named Rose. When Rose found out that Katerina had escaped from Klaus with the moonstone, she locked her in a room and told her that she would take her back to Klaus as soon as the opportunity arose, not wanting to suffer Klaus' wrath. Katerina tried to commit suicide by stabbing herself with a knife, saying she would rather die than go back to Klaus, but Rose force-fed her some of her blood to heal her. When Rose turned her back to confront Trevor, Katerina hung herself with a rope. Later, when Katerina woke up in transition, Trevor asked why she did it and claimed he would have helped her live. Katerina responds by saying that he would have been able to help her run and that running was never going to be enough.

Rose then explained to Trevor that Katerina used him to escape, and, knowing Klaus would find out their role in the escape, Rose attempted to kill Katerina with a stake. Katerina used the owner of the cabin as a shield, which resulted in her death. Katerina then gave in to her instincts and drained the little old lady, completing her transition into a vampire. She then threw the body toward Rose and Trevor and fled into the night. Katerina returned to Bulgaria in the later months of 1492 to find her entire family brutally slaughtered by Klaus. She knew he had done it as revenge for her escape and subsequent transition. She was last seen weeping over her mother's dead body.

Katherine may have stolen the spell for making Daylight Amulets from Esther's grimoire before fleeing from Klaus as this may explain how Emily was able to make Katherine, Bethanne, Pearl, Anna, and Harper daylight rings and her a necklace in 1864.

Sometime during 1498, Katherine returned to Bulgaria after escaping from Klaus. Katherine searched every village and cottage for her daughter, Nadia Petrova, who was eight at the time but had no luck in finding her.