Sycorax

"Sycorax strong, Sycorax mighty, Sycorax rock, as in the modern sense, they rock."

During a live broadcast following Guinevere One’s journey to Mars, the British space probe was intercepted by a giant spaceship. When viewers across the world tuned in expecting to see images of the red planet's surface, they were instead met with the skull-like visage of the Sycrorax!

Beneath their helmets, the Sycorax are skinless, their features enclosed within a bone-like exoskeleton. A race of blood-thirsty warriors, they planned to enslave the people of Earth by holding one third of the population hostage through the use of blood control. Everyone with A-positive blood climbed to the highest point they could reach, ready to jump at the Sycorax's command. However, the Tenth Doctor called the Sycorax's bluff, calling blood control "a cheap bit of voodoo."

Freshly-regenerated, the Doctor challenged the Sycorax leader to a sword fight to decide the fate of the Earth. Losing a hand in the process (and then growing another), he defeated the alien with the nifty use of a satsuma. As champion, he commanded the Sycorax to leave the Earth and never return. However, as their ship was leaving, Prime Minister Harriet Jones instructed Torchwood to shoot it down as a warning to any other aliens planning an invasion. The human race is drawing attention to itself...