The Zygons are a fictional extraterrestrial race in the long-running British science fiction television programme Doctor Who. The Zygons have shape-shifting abilities, allowing them to replicate the appearance of another being, but they must keep the subject alive in order to use its body print. Limited by the small size of their force, they rely on shape-shifting and their organic space craft to conceal their numbers and seize power on Earth. Tenth Doctor actor David Tennant has stated that they are his favourite monsters from the show.