Kallen Kōzuki (紅月カレン Kōzuki Karen) is one of the main characters featured in Code Geass: Lelouch of the Rebellion, as well as one of the two protagonists of Code Geass: Lancelot & Guren. She is officially known as Kallen Stadtfeld (カレン・シュタットフェルト Karen Shutattoferuto), and goes by this name at school, but prefers her mother's maiden Japanese name during her revolutionary (now military) activities.

Ami Koshimizu won Best Actress in supporting role for her role as Kallen at the first Seiyuu Awards in 2007. Kallen was awarded 8th place in the 29th Anime Grand Prix, then 17th and 16th, respectively, in the following two.