Master Chief (Halo)
MCPON John-117, or "Master Chief", is a fictional character and the protagonist of the "Halo" fictional universe created by Bungie. Master Chief is a playable character in the series of science fiction first-person shooter video games "", "Halo 2", "Halo 3", "Halo 4", and "". Outside video games, the character appears in books and graphic novels—"", "", "", and ""—and has cameos in other "Halo" media, including "", "", "The Halo Graphic Novel", "Halo Legends" and "".
Gravemind
Gravemind is one of the primary antagonists of "Halo 3". While the Master Chief and Arbiter have returned to Earth in order to stop the Prophet of Truth, the religious leader of the Covenant, from activating a Forerunner artifact buried in Africa, Gravemind turns "High Charity" into a Flood hive and sends an infected cruiser to Earth in an attempt to infest the planet; this plan fails, and a message from Cortana informs the Master Chief and allies of the existence of the Ark, a special installation built by the Forerunners outside of the Milky Way galaxy where "all" the Halos can be fired remotely. Gravemind, the Arbiter, and the Master Chief all want to stop the High Prophet of Truth from activating the rings, so the Flood once again ally with the Chief and Arbiter. As soon as Truth is killed, however, the Gravemind betrays both the Master Chief and the Arbiter, The Chief escapes the Flood's clutches and rescues Cortana from "High Charity". Despite being tortured by Gravemind, Cortana has managed to keep a secret safe from the Flood; she has the activation index of Installation 04, which she captured from 343 Guilty Spark during "". Using the index, Cortana can activate the local ringworld, destroying Gravemind and the Flood, but sparing the galaxy's sentient life. Gravemind finally gains this knowledge, but too late; the Master Chief escapes with Cortana, destroying "High Charity" in the process. Gravemind survives the blast and attempts to rebuild himself on the new ring. Despite his best efforts, the Master Chief and company activate Halo, destroying it and defeating the Flood once again. Resigned to his defeat, Gravemind nonetheless insists that it will only slow—not stop—the Flood.