The Brain of Morbius.

Morbius was an evil timelord. He was captured by the Timelords and sentenced to death by atomization for his many crimes. Before this sentence could be carried out, the Morbius cult stole his brain from his body and Mehendri Solon preserved it on the planet Karn where the Timelords weren't supposed to watch due to the Sisterhood of Karn. The Timelords atomized his body only. Solon made a "frankenstien" monster of various forms of life that crashed on Karn to house the Brain. The Head was the only thing missing.