On July 9, 1762, Grand Duchess Catherine Alekseyevna (Catherine the Great) led a coup that ousted her husband Peter III. 

“Had it been my fate to have a husband whom I could love, I would never have changed towards him.” 

275th Birth Anniversary of Catherine II (The Great)
Part of the History of Russian State series
Issued by Russia in 2004
Designer: Alexander Kernosov

If you are are looking for a quick primer on Catherine, try Catherine the Great: sex, slander and absolute power | Art UK. It’s approachable and fascinating. BBC’s page is factual, if a bit bland BBC – History – Catherine the Great. 
The True History Behind ‘The Great’ and Catherine the Great | Smithsonian (smithsonianmag.com) is a good place to separate the myth and nonsense behind her story.