Great Intelligence

Dr. Walter Simeon is a man associated with the Great Intelligence. He is the primary antagonist of the Doctor Who episode, "The Snowmen".

Biography
As a young boy, Walter did not want to make friends, and ultimately he stumbled upon the Great Intelligence, pouring his darkest thoughts out. As he got older, he began building an army of ice for it, upon its command, unknowing that it was actually his thoughts reflected.

In Simeon's later life, the Doctor stumbled upon this, and recognised the Great Intelligence from a previous encounter. He was able to explain what was happening to Simeon, and forced him to be bitten by a memory worm, removing all memory of his adult life. However, the Intelligence was independent enough to continue on its own. It tried to take control of Dr. Simeon's body, however the Doctor was able to force the Intelligence to give it up, albeit killing Dr. Walter Simeon in the process.