BODACH

The Bodach were incorporeal creatures who  fed on the energy produced by a mind when dreaming. They could emit psychic energy which would cause nightmares, allowing them to feed. This psychic energy could be blocked by aluminium. As the Bodach had no body, they were forced to control these sleeping people, using them to interact with their surroundings. The Bodach were known to the Celtic people, who believed they were evil spirits. At some point, an Obelisk was made with two crystal eyes. With these crystals, the Bodach would be able to send the whole world to sleep and feed on their dreams. In unknown circumstances, this did not come to pass, and instead the obelisk was buried outside what would be London. In 2050, the site was dug up and the obelisk destroyed shortly after.

Source: Doctor Who Universe (K9TV: Dream-Eaters)