The Flood is a fictional parasitic alien lifeform and one of the primary antagonists in the Halo multimedia franchise. First introduced in the 2001 video game Halo: Combat Evolved, it returns in later entries in the series such as Halo 2, Halo 3, and Halo Wars. The Flood is driven by a desire to infect any sentient life of sufficient size; Flood-infected creatures, also called Flood, in turn can infect other hosts. The parasite is depicted as such a threat that the ancient Forerunners constructed artificial ringworld superweapons known as Halos to contain it and, as a last resort, to kill all sentient life in the galaxy in an effort to stop the Flood's spread by starving it. The Flood's design and fiction were led by Bungie artist Robert McLees, who used unused concepts from the earlier Bungie game Marathon 2. The setting of the first game, the ringworld Halo, was stripped of many of its large creatures in order to make the Flood's surprise appearance more startling. Bungie environment artist Vic DeLeon spent six months of pre-production time refining the Flood's fleshy aesthetic and designing the organic interiors of Flood-infested spaceships for Halo 3. The player's discovery of the Flood in Halo: Combat Evolved is a major plot twist, and was one of the surprises reviewers noted positively. The Flood's return in Halo 2 and Halo 3 was less enthusiastically praised. Reaction to the Flood has varied. While some critics have described the Flood as derivative or clichéd, others have ranked it among the greatest video game villains. Development The Flood is depicted as a parasitic organism that infects any sentient life of sufficient size. The largest self-contained form that the Flood can produce itself without using other biomass is an "infection form". These forms seeks hosts, living or dead, and attempt to drive sharp spines into the host and thereby tap into the nervous system. The host is incapacitated while the infection form burrows into the host's body and begins the mutation process, bringing the host under Flood control. Depending on the size or condition of the body, the infection form mutates the hapless host into various specialized forms in the continual drive for more food. Larger hosts are turned into forms for combat, growing long whip-like tentacles, while mangled and disused hosts are turned into incubators for more infection forms. The Flood also creates forms known as