The War Chief

The War Chief, known at the Time Lord Academy as Magnus, was a former friend of the Doctor. He became a renegade Time Lord who assisted the War Lords. After the failure of the War Lords, he regenerated, although he was deformed by the experience. He travelled back in time to use the Nazis as his agents. He was finally stopped by the Seventh Doctor.

Life on Gallifrey
Magnus belonged to the Deca, the same Academy clique as the First Doctor, serving as a leader of the group with a particular interest in the construction of TARDISes. He had an attraction to Ushas, and was once warned away from her by Mortimus. He became fascinated with a race the Time Lords had once banished from Gallifrey, wanting to use time travel for use in their games of war.

After the disappearance of Rallon and Millennia, Magnus was appointed to the scientific research department for the rest of his time at the Academy. He stood by the Doctor while he was held accountable for their disappearance. (PROSE: Divided Loyalties)

The Doctor once advised Magnus to reserve his regenerations, but Magnus did not listen as he was not concerned. (PROSE: Invasion of the Cat-People) He even mocked the First Doctor for "still hobbling about in [his] old body". (COMIC: Flashback)

Magnus became an ambitious and arrogant Time Lord with little time for "Theta Sigma". He took part in a scheme to provide Gallifrey with a new power source derived from a sphere of artron energy. He hoped to revitalise the decadent Gallifreyan society. The Doctor made himself an unwelcome observer of the experiment. He realised the sphere was a living being and that Magnus' actions were killing it. He sabotaged Magnus' equipment and freed the creature, for which the Time Lords commended him. This angered Magnus even more. The Doctor and Magnus were bitter enemies from that day on. (COMIC: Flashback)

Magnus soon began to rise rapidly in the Time Lord hierarchy. So much so, that Cardinal Borusa saw him as a threat to his own position of power, and persuaded the Celestial Intervention Agency to manufacture evidence of treason against him. Believed to be a criminal, Magnus fled from Gallifrey, became a renegade and swore revenge on the Time Lords. (PROSE: Timewyrm: Exodus)

Ally of the War Lords
Now calling himself "the War Chief", he worked with the War Lords. They abducted soldiers from wars spread across Earth's history for simulated versions of the wars from which they came. Thinking humans the most vicious species in the galaxy, the aliens hoped to pit the survivors against each other and use them to conquer Mutter's Spiral.

The War Chief aided the War Lords by helping them build SIDRATs, TARDIS-like space-time machines. They used them to kidnap the human soldiers and travel between era-specific zones which they had created. The War Chief and the Second Doctor met and recognised each other. The War Chief solicited the Doctor's help to double-cross the War Lords and seize power for themselves. The Doctor pretended to accept the War Chief's offer. (TV: The War Games)

The Security Chief of the operation distrusted the War Chief, believing he meant to call in the Time Lords. The two engaged in a series of machinations against each other which ended with the War Chief disgraced. He shot his rival dead. Unable to resolve matters nor return the soldiers to their own times, the Doctor summoned the Time Lords for aid, while the War Lords uncovered the War Chief's plans and executed him. (TV: The War Games) Unknown at the time, while the War Chief remained on the War Lords' ship, the War Chief did not die but, rather, underwent a faulty regeneration. His new form looked like two bodies fused together. He took to wearing cloaks and hoods to disguise the fact, eventually convincing the War Lords that his 'betrayal' of them was just a misunderstanding. (PROSE: Timewyrm: Exodus)

Aftermath
Having helped the War Lords to break the time loop the Time Lords had erected around their world, the War Chief helped them travel to Nazi Germany. He served as an occult advisor to Adolf Hitler under the name "Doktor Felix Kriegslieter", hoping to change history with the Nazis as his agents, believing that they were so vicious that they barely needed the War Lords' conditioning. (PROSE: Timewyrm: Exodus) One time, concerned with Hitler's health, Martin Bormann telephoned him. (PROSE: Players) The Seventh Doctor later confronted the War Chief, prompting him to try to take the Doctor's healthy body and his six remaining regenerations. However, his efforts to replace Hitler with Heinrich Himmler was thwarted by Himmler's devotion to his Führer. This allowed the Doctor to alert Hermann Goering to "Kriegslieter's" betrayal and destroy the War Chief's base by overloading its nuclear reactors, the brainwashed Nazis falling to the superior initiative of their mentally free opponents. In the final moments before Drachensburg castle collapsed, Ace looked down and saw the War Chief engulfed in flames, no longer malformed but appearing as his "young, tall, dark and satanically handsome" self. (PROSE: Timewyrm: Exodus)

Personality
The War Chief was an ambitious and arrogant individual, cunning, and with great tactical abilities. He pretended to serve the War Lords loyally, while plotting to take control of them. He also made feuds easily. (TV: The War Games) He was unconcerned about using up regenerations and never listened to the Doctor, who advised him not to waste them. Behind the War Chief's actions lay real idealism, tainted with power lust. (PROSE: Invasion of the Cat-People)

Behind the scenes

 * FASA's The Doctor Who Role Playing Game in the module Legions of Death identified him as a renegade Time Lord who is a former ally of the Time Lord known both as the Monk and the Master, and, having survived the events of the War Games by using one of his SIDRATs to reach his TARDIS, he later attempts to take over the Roman Empire. This module also states that until the War Games, he was working for the Master but that the War Chief considers both the Doctor and the Master to be responsible for his defeat.
 * The necklace prop the War Chief wears in The War Games is the same prop previously worn by Zephon in The Daleks' Master Plan.
 * Although Magnus was never called anything but War Chief in his only televised story, there was no evidence that this was a regular moniker or modus operandi. Usually, during the story, the term War Chief was treated more as a title instead of a name.
 * In 1992, the comic strip Flashback depicted the First Doctor and Magnus back on Gallifrey, and ending their friendship when Magnus callously used a sphere of Artron energy that was actually a harmless lifeform as a fuel source for his experiments. Magnus was immediately identified by most readers as a younger version of the Master, or by some as the War Chief. However, DWM refused to comment either way.
 * The War King is hinted to be the War Chief in The Book of the War; he is also suggested to be the Master, apparently confirming the ages-old theory that they are the same character.