The android maker lived on Calderon IV.
He was involved in a coup on Calderon IV that was defeated by the Third Doctor and Sarah Jane Smith. He was believed dead. He had possession of the communication device the Doctor had left behind.
He created an android that perfectly resembled the Doctor. It had an explosive in its head. The plan was for the android to kill the Doctor when he arrived and replace him, then address the Presidium, detonating the bomb there.
The android maker's plan was all for nothing, however, because when the Doctor arrived, he had a different face. (PROSE: The Android Maker of Calderon IV)