BORN: Before 9,000,000 BCE
The Gravemind is the central brain behind the Flood, though it is not so much a central commander as it is the mind of all Flood forms, including infection forms, carrier forms, and combat forms. Though graveminds have usually interacted with humanity one at a time, there can be many graveminds in the galaxy at any one time, which all share the same intelligence. Graveminds have been found by humans on both Delta Halo during the Battle of Installation 05, and on the Ark during the Second Ark Conflict.
Many Graveminds existed during the later stages of the Forerunner-Flood War, though they would often interact with Forerunners as if they were a single mind such as was done with the Ur-Didact. It is thought that the Primordial, a creature discovered by ancient humans during the Human-Forerunner Wars, shared the same mind with any and all Graveminds that came after the Primordial’s destruction by the IsoDidact, though that has never been definitively proven.