Katerina Petrova aka Katherine Pierce is a Petrova doppelgänger and a major antagonist in The Vampire Diaries. She serves as the true primary antagonist of season 1 (alongside Damon Salvatore, who was the main antagonist for the first two chapters), the main antagonist of Season 2 (alongside Niklaus Mikaelson), a supporting anti-heroine of Season 3, the tertiary turned true secondary antagonist of Season Four and a protagonist villain turned temporary main antagonist of Season Five, where she joined the main characters. She is a vampire who was the lover to the Salvatore brothers, which may have caused their feud. She is the ancestor of the series' heroine Elena Gilbert. In the Season 4 finale Graduation she is forced to have the Cure by Elena which made her human (later found out that her