Azaxyr

Commander Azaxyr (Demoted to Captain Azaxyr in Season 15) is an Ice Lord who first appears in the third episode of Season 11. He seems to help the humans fight off the Cybermen on the planet Weblus, but it turns out he's actually the secondary antagonist who is working for the Cybermen in Season 12. In the season 13 finale, however, he becomes an anti-hero.

Role
Azaxyr first appears as an Ice Lord who wants to prevent the humans on planet Weblus from becoming Cybermen. When he arrives in his spaceship, he declares himself the planet's "Judge, Jury and Executioner". When he asks the Doctors where Skaldak is, the Ninth Doctor tells him of Skaldak's sacrifice to stop the Daleks from escaping Spiridon. Azaxyr replies that he had a great deal of respect for Skaldak and that his death is tragic.

After the First, Seventh, Eighth, War, Ninth and Twelfth Doctors are captured by the Cyber Controller at the end of Season 11, Azaxyr (who brought the survivors to Peladon) tells the remaining Doctors to train a group of soldiers to fight the Cybermen.

In the fifth episode of Season 12, Azaxyr reveals that he is working for the Cyber Controller and that all the survivors he helped to "save" were actually being handed into the Cybermen's clutches.

In the fifth episode of Season 13, it is revealed that Azaxyr is working for the Cyber Controller because if he refuses, then he will kill Iraxxa, who he is holding as prisoner.

In the Season 13 finale, he betrays the Cyber Controller after he is reminded of Skaldak's legacy by the Tenth Doctor (as well as a motivational speech from Iraxxa), and says to him "I am not a Commander, I am a monster, just like you." When the Controller tries to kill him, Commander Titus, who is being converted into a Cyberman, impales his arm with a Sonic Lance which the Sixth Doctor gave to him. After the Controller kills Titus, Azaxyr blasts the Controller with his sonic blaster, killing him. After this, Azaxyr leaves with Iraxxa.

In Season 15, Azaxyr (now demoted to Captain) assists Iraxxa in helping the Doctors stop a Dalek plan to infect every life form in the Universe with Dalek nanogenes.