The Ood are slaves in the future but they were Possessed by The Beast and the Ood Brain
The Ood are Squid like creatures from the Planet of Ood-Sphere. They were first working for Sanctuary Base as Slaves when the Planet was being sucked into a Black Hole. The Ood were Peaceful until the Beast possessed them all. They Killed People by using a Sphere like Ball. In the end they were all Killed because of the Black Hole.
They then appeared on their Home Planet of Ood-Sphere they Cold and Snowy Planet. They went Rabid and Red Eyed because of the Ood Brain. They attacked the Bases Workers and killed them all because they were Slaves. When the Ood Brain Shut Down the
Ood were Free and they could Sing their Song again but Ood Sigma had turned their Evil Master Klineman Halpen into one of them as he was Human before.
Then Ood Sigma appeared years later and he told The Doctor they had Bad Dreams. The Dreams were of the Evil Time Lord the Master and some with Donna, Wilfred and Lucy Saxon of the Dark Ages.
They have appeared in Series 2: The Impossible Planet and The Satan Pit.
Then in Series 4: Planet of the Ood.
Then in 2009 Specials: The Waters of Mars and The End of Time.