Morbius

Morbius was a formerly high-ranking Time Lord whose career ended in destruction and ignominy, and escaped a sentence of death only by means of a secret brain transplant. The Fourth Doctor and Sarah Jane Smith encountered him during the events of the TV story The Brain of Morbius; the Fifth Doctor met him during the events of the novel Warmonger.

Life and career
Morbius' ambition led him to become the head of the High Council, where his warlike nature led him to urge the Time Lords toward a policy of conquest. When the Time Lords rejected him, he formed an army of his own composed of both dedicated followers and mercenaries. He promised his followers the secrets of time travel and immortality. He sent them into battle across many worlds, including the planet Karn, where he hoped to seize the secret of the Elixir of Life guarded by the Sisterhood of Karn. He was captured with the assistance of the Sisterhood and brought to trial on Karn. He was sentenced to be executed by disintegration for his crimes, and his body was indeed destroyed, with Sisterhood leader Maren in attendance. However, Morbius escaped death when one of his followers, the human surgeon Dr. Mehendri Solon secretly removed the Gallifreyan criminal's brain before his disintegration. Solon took the brain and went into hiding on Karn, where he began planning to build a new body for Morbius out of parts salvaged from corpses found in the wreckage of spacecraft which the Sisterhood had caused to crash on the planet as their way of protecting the Elixir.

The Brain of Morbius
The Doctor and Sarah Jane Smith landed on Karn and stumbled upon Solon's castle just as Solon was completing Morbius' new body, leading them to discover Morbius. Although the Doctor had not previously met Morbius in person, he did recognize Morbius' telepathic brain pattern.

Morbius's new body was horrifyingly grotesque, leading the Doctor to mock him as "Chop Suey, the Galactic Emperor!" But Solon's ability to merge alien tissues together did give Morbius at least a few advantages over his previous biological form, including lungs from a Birastrop capable of withstanding cyanide. Other parts of Morbius' body included a human left hand which came from Solon's unknowing assistant Condo, a giant lobster-like right hand, and a humanoid torso. The body Solon had built lacked one important element, namely a head suitable for storing the unique and delicate properties of a Time Lord brain. Solon required the head of another Time Lord in order to safely house Morbius' brain, but when plans to use the Doctor's head failed and the container holding the brain was spilled, he resorted to an unproven, experimental braincase which included two stalklike eyes.

This braincase was prone to developing a static charge, a weakness exploited by the Doctor by challenging Morbius to a Time Lord mindbending contest. It is not at all clear who won the contest, but it was costly for both Gallifreyans. The Doctor collapsed from the strain, and Morbius' brain appeared to be damaged by a static shock. During the contest, images of the Doctor's previous three incarnations appeared in the air above them, as well as a number of images of others whose identity is disputed. It is possible that the unknown faces belong to previous and otherwise unexplained incarnations of the Doctor, suggesting that the incarnation known as the First Doctor was not, in fact, his first incarnation. However, it is also possible that the faces belong to previous regenerations of Morbius -- or that they are memories of entirely different people drawn from the minds of either the Doctor or Morbius.

After the battle, Morbius appeared to be left in a dazed, animalistic state. He did not speak again during the story, and only uttered seemingly agonized sounds of anger and pain. Leaving Solon's castle, he was chased by the Sisterhood over a cliff, where he was apparently killed.

Appearances in other media
Morbius's war against the Time Lords and his execution (including how Solon saved his brain and the Fifth Doctor's involvement) are depicted in the Past Doctor Adventures novel Warmonger by Terrance Dicks. The canonicity of the novels is uncertain.