The Zygons

The Zygons are an alien race covered in sucker-like protuberances, and their semi-organic spaceship crashed in Loch Ness. They possessed a chameleon-like ability to adopt the form of their human prisoners. The Zygons planned to restructure the Earth in order for their invasion fleet comes to make a full-scale colonization. The Doctor was taken prisoner by them and held in their spaceship. The Doctor managed to activate the self-destruct on the spaceship and destroyed them all. Broton was the leader of the Zygons and copied the Duke of Forgills body to get into the National Energy Conference. He was then shot by the Brigadier will he was attempting to kill all of the people of Earth.  

The Zygons only appeared in The Terror of The Zygons.          

The pictures above show how a Zygon (Broton) transforms from his figure into a body print of a human. They have to use the body print every few hours so it does not become lost. They got all of their prints from capturing prisoners and keeping them in their spaceship.