343 Guilty Spark, also referred to simply as Spark or as The Monitor, is an AI Monitor created by the Forerunners and one of the main antagonists of the Halo series. He is left to watch over Installation 04 and its contents when the Forerunners departed. He appears as the main antagonist of Halo: Combat Evolved, an anti-hero in Halo 2, and the secondary antagonist of Halo 3. As with UNSC and Covenant artificial intelligences, Guilty Spark's programming prohibits certain actions outside of his function. He cannot, for example, retrieve the Index from the Library or unify it with the Core, instead needing a Reclaimer to carry out this task.