Ood Brain

The Ood Brain was a huge living brain that under natural circumstances controlled the connection between individual Ood, facilitating their Hive mind. It was capable of telepathically reaching Ood over the distance of three galaxies. It is shown to be living as Klineman Halpen threw Ryder on to it and it swallowed him. Whether or not he knew it would do this is unknown.

Biography
A few centuries before the 42nd century, humans discovered the brain beneath the Northern Glacier on the Ood Sphere. By 4126 it was contained in warehouse 15 of Ood Operations, surrounded by a telepathic barrier so it couldn't communicate with the Ood. It was kept alive, even though it had to be contained, because without it the Ood would die. The neutralisation of the brain, together with lobotomising the Ood, allowed them to enslave Oodkind. Dr. Ryder, an agent working for Friends of the Ood, managed to infiltrate Ood operations and after years of patience came into a position where he could covertly lower the intensity of the field, which first manifested itself as Red-eye and later resulted in a full-blown Ood rebellion. The Doctor eventually shut off the barrier freeing the Ood from slavery.

In previous encounters, Red-eye in the Ood had indicated posession by a stronger mind. On the Ood Sphere it was a manifestation of the Ood Brain's desire for revenge. Prior to Doctor Ryder's help, the Ood Brain could only make contact with a few Ood. Afterward, its influence spread to the entire planet. The different behaviour patterns in the Ood during Planet of the Ood were a manifestation of the Brain's telepathic link, with the "rabid Oods" representing its anger. Ood Sigma however, seemed to be the focus of the Brain's patience and intellect, which allowed him to function as an individual despite the fact he had a translator orb; and subsequently allowed him to surreptitiously convert Halpen into Ood. (DW: Planet of the Ood)