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. 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. However, mention is made of 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 them 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". 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)

Encounter with the Tenth Doctor
When encountered by the Doctor and Rose Tyler, the Ood were part of a human-led expeditionary force on the planet Krop Tor, orbiting black hole K37J5. 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 his "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)