Arkallax

 was a commander of an army. He eventually settled in a tower block on Earth. He was intrigued with the Seventh Doctor's mind. He later enticed Melanie Bush and Ace. He could read minds. His mind wasn't in his original body. He told Ace and Mel that he was the last of his kind and that he was stuck in a bubble. He took the mental energies from the people in the tower block to find a way out. He had become the tower block. He tried to possess the Doctor but he fought back. He also used his abilities to manipulate the tower block to stop Mel, Ace and Isobel. (AUDIO: The Dispossessed)