Great Intelligence

"Now, the dream outlives the dreamer and can never die. Once, I was the puppet. Now I control the strings!"

- The Great Intelligence, taking control of Dr. Simeon.

The Great Intelligence, also known as Yog_Sothoth, is an entity who has been among the Doctor's many enemies in the series Doctor Who. However, while introduced in the 1967 episode "The Abominable Snowmen", the Great Intelligence's origins are revealed in the 2012 episode "The Snowmen" and he acts as the main antagonist of season 7 of the new series.

He was voiced by Ian McKellen in "The Snowmen", and was portrayed by Richard E. Grant (who initially played his host, Walter Simeon) for the rest of the series.

Biography
From another world, the Great Intelligence came to 1800s London during winter and formed a mental link to a child named Walter Simeon to survive. With the adult Dr. Simeon finding the Great Intelligence Institute to house the preserved snowman he inhabited, the Great Intelligence build an army of snowmen to enhance. However, the Eleventh Doctor, having faced the Great Intelligence in his Second incarnation, knew what he was dealing with and used a memory worm to render Simeon mindless. However, the Great Intelligence became independent enough to continue on his own and possesses Dr. Simeon's brain dead body to kill the Doctor before being forced to leave it.

The Great Intelligence also possessed the body of the High Lama Padmasamabhava in 1935, having enabled the Lama to live for over 300 years. The Great Intelligence plans to create a physical body for himself in the form of robot Yeti that the Second Doctor and his companions defeat. The Great Intelligence retaliates years later by possessing Staff-Sergant Arnold while having his army of Yeti take over the London Underground while spreading a deadly web through London, all to lure the Doctor and drain his mind before being driven back. In the 21st Century, the Great Intelligence acted through a woman called Miss Kizlet using an organization based at the Shard to collect and harvest the minds of people using the wifi. The Eleventh Doctor manages to free his victims, with the Great Intelligence satisfied with what he learned as he has Miss Kizlet wipe all memories of his existence from her mind and others in order to hinder UNIT's investigation.

Having acquired data on the Doctor's actions over the years, the Great Intelligence makes his move using the spectral Whisper Men as vessels that assume the form of Dr. Simeon. The Great Intelligence kidnaps the Silurian Vastra, Jenny and the Sontaran Commander Strax, taking them to Trenzalore to lure the Eleventh Doctor to his tomb the dying TARDIS to open it. He threatens to use the Whispermen to kill the Doctor's friends unless the Tomb was opened, but a Data Ghost of River Song opened the TARDIS. Inside, a temporal rift representing the Doctor's timeline has manifested. There, knowing it would destroy him in the process, the Great Intelligence scatters himself along the Doctor's timeline and rewrites it to destroy the Doctor and all the good he has done, which starts destroying the Universe and erases Jenny and Strax. However, the Doctor's Companion Clara Oswald also scatters herself along the timeline to undo most of the damage.