Ood

The Ood are a humanoid species with coleoid tentacles on the lower portions of their faces. By the year 43K2.1, the Ood were a slave race to Humanity, performing menial tasks, and it is claimed that every Human has an Ood servant. They are generally barely even regarded as being alive, and are considered to be expendable. The Ood offer themselves for servitude willingly, having no goals of their own except to be given orders and to serve. It is also claimed that they cannot look after themselves, and if they do not receive orders, they simply die. Despite this there is a group called the "Friends of the Ood" who are apparently lobbying for Ood freedom. (DW: The Impossible Planet)

The Ood require a translator device, a small sphere connected to their "mouths" by a tube, to facilitate speech between Ood and Humans. There appears to be no gender differentiation among the Ood, and they say they require no names or titles as they are "one", but they do have designations such as Ood 1 Alpha 1 (though these appear to be assigned to them by their human masters). The Ood are empaths, sharing among themselves a low-level telepathic communication field, rated at "Basic 5" (with "Basic 30" being the equivalent of screaming and "Basic 100" meaning brain death). (DW: The Impossible Planet / The Satan Pit)

The Ood and the Beast
When encountered by the Doctor and Rose Tyler, the Ood were part of the Walker Expedition. Unlike the humans or the Doctor, the Ood knew of prophecies regarding the Beast which the expedition would later discover. (TS: Tardisode 8, Tardisode 9, DW: The Impossible Planet)

The empathic nature of the Ood seemed to make them susceptible to psychic possession by the Beast, who formed the Ood on the base into its "Legion". While possessed, an Ood electrocuted a human guard by throwing its translation sphere at him. (DW: The Impossible Planet)

The Ood were defeated when Danny Bartok, the expedition member in charge of them, broadcast a telepathic flare which reduced their field to "Basic Zero", creating a "brainstorm" which caused them to collapse. However, their telepathic field began to reassert itself after a time. When Krop Tor was sucked into the black hole, the Doctor was unable to save any of the Ood on the base, who had been freed of the Beast's control, and all of them perished. (DW: The Satan Pit)