Human-Time Lord Meta-Crisis

Human-Time Lord Meta-Crisis was the term applied to a hybridised organism that combined the traits of a Time Lord and a human.

The first known instance of a Human-Time Lord Meta-Crisis to take place in the Doctor's life occurred during his third incarnation Overseer Zim attempted to wipe his mind using a mind thresher. After he thought the Doctor's consciousness had been completely wiped, he placed the human mind of Grubenfeuer Hans Vogel inside of his brain. Due to the complexity of a Time Lord mind, however, Zim was unable to completely eliminate all traces of the Doctor's consciousness. This resulted in a Meta-Crisis which threatened to destroy both the Doctor and Vogel's minds. In the end, the Doctor was able to remove Vogel from his mind by sabotaging Overseer Zim's facility. (AUDIO: The Hidden Realm)

The DoctorDonna was an example of a human with a Time Lord consciousness. The Tenth Doctor stated that a Human-Time Lord Meta-Crisis had never happened before because it was unsustainable. Donna had to be reverted to her human self; her brain could not hold a such a consciousness. The Doctor erased her mind of all knowledge of him. (TV: Journey's End) Despite this, Donna's latent consciousness retained at least some non-human aspects, protecting her when turned the world into copies of himself. Apparently, it also subconsciously guided her to buy a book for her grandfather, which led the Doctor and him to Joshua Naismith. (TV: The End of Time)

The Meta-Crisis Doctor seemed to be a mixture of the two races. He did not burn up, presumably having a Time Lord brain, but only had one heart and could not regenerate. He also showed quirks of Donna Noble, the human with whom the Meta-Crisis had occurred, specifically her urge to argue and say "Oi!". (TV: Journey's End)