Who is Louka in Arms and the Man?

Louka is an ambitious and sometimes spiteful maid. She is desperate to rise above her station, and she is attracted to Major Sergius Saranoff. Sergius, however, is engaged to Raina, and he is a gentleman, whereas, she is just a servant. Louka shames Sergius about the hypocrisy of his behavior and tries to break up his relationship with Raina. In the end, she wins her man.