The Sycorax are a tribal species of warriors and plunderers known to build their starships out of asteroids and manipulate other races into surrendering to them through technology resembling magic, such as blood control.
The Sycorax have an endo and exoskeleton, causing them to appear skinless but largely covered with bone formations. Despite their tribal and superstitious society, the Sycorax possess advanced technology including electrified whips capable of reducing their enemies to charred skeletons, teleportation and the means of mind controlling others, provided they have a sample of the victim's blood type.
During Christmas 2006, a Sycorax tribe invaded Earth after abducting the Guinevere one space probe, containing records of human history, cultures and a sample of A+ blood. Using this, the Sycorax placed every human of this blood type under their control, threatening to force them into committing suicide if the rest of humanity did not submit to enslavement. Upon detecting a type 40 TARDIS on Earth and teleporting it aboard, the Sycorax leader was confronted by the Doctor, the only Time Lord known then to have survived the Time War. Upon deactivating the blood control, the Doctor challenged the Sycorax leader to a sword duel to decide the fate of Earth. Although the Sycorax leader severed the Doctor's hand, only for him to immediately grow a replacement, he was defeated and agreed to spare the Human race. Despite this, and the Honourbound nature of the Sycorax, he broke his word and attempted to kill the Doctor with his back turned, forcing the Time Lord to kill him.
With the Doctor's warning that Earth is defended, the remaining Sycorax agreed to leave the planet in peace. However, Harriet Jones, the prime minister of Great Britain at the time, ordered the use of salvaged alien weaponry to destroy the Sycorax ship as it fled Earth as a warning to other races who may be a threat to Earth. Enraged by this, the Doctor arranged for Jones to be removed from office, asking her assistant "Don't you think she looks tired?" with the knowledge that this would cause widespread public doubt about her capability as Prime Minister.