Star Wars: Episode III - Revenge of the Sith (2005)

In one of the final battles of the ongoing Clone Wars, Obi-wan Kenobi and Anakin Skywalker engage Dooku in an attempt to rescue Lord Palpatine. Prodded by Palpatine Anakin beheads an unarmed Dooku to begin his descent to the dark side. Obi-Wan Kenobi is then sent to take down the leader of the droid army, General Grevious, and end the Clone Wars. Meanwhile, the secrets of the Dark Side of the Force are too much for Anakin to deny as the Evil Lord Sidious tempts him to turn against his master and his allies.