IMHO the title character in Empress Ki is the single strongest female character in cinema. Ha Ji Won does a spectacular job portraying a woman who is super tough, brilliant, and beautiful. In 51 episodes she fights her way through all obstacles from Korean slave girl to the unchallenged power behind the throne as the Empress of China. She's the most unusual character I've seen in historical k-dramas because she can fight with the best of the men, while outmaneuvering, out-thinking and ultimately destroying all of her much more powerful enemies. In most dramas, the heroine is protected by the hero. In this drama, she protects the Crown Prince and Emperor. Yet in spite of her strength, she remains attractive as a woman, which is a difficult combination of qualities for an actress to achieve.
This is one of the few dramas that I've re-watched over and over starting at random episodes because the whole thing is so intense. Many other reviews have described this drama in much detail, so I won't repeat what has already been said. Actress Ha Ji Won is one of Korea's most successful and accomplished actresses, and I think this will be remembered as her signature role.
When I finally discovered Korean dramas, I completely gave up Hollywood, and since then have watched over 200 k-dramas and movies. While there are many good ones, there are only a couple which are at the absolute top of my list. It's almost impossible to compare modern and historical dramas, but among (mostly) modern dramas, this one is at the top of my list. It has everything one could want in a drama. It's counterpart at the top of my historical drama list is Empress Ki. These dramas star two of Korea's top actresses, who demonstrate convincingly why they have that status.