Kotris

Straxus was a Time Lord who worked for the High Council of Gallifrey.

Biography
Straxus once worked for the Celestial Intervention Agency. Unbeknownst to the High Council, he was instructed to gather from the Vess weapons that would allow the Time Lords to defend themselves and defeat races that posed a threat to Gallifrey. He was discovered by the Master, who blackmailed him and the CIA to by threatening to inform the High Council. In exchange of his silence, Straxus let him buy a conceptual bomb from the Vess. The Master used the device to attack the Doctor's timeline, thus threatening the whole universe. Straxus then captured the Sixth Doctor to ask for his help in defeating the Master and, eventually, regretted his own behaviour and meant to report to the High Council. In this situation, his own TARDIS was sacrificed and destroyed by the Sixth Doctor by forcing and expanding its dimensional stabilisation field, in order to let other three incarnations of the Doctor to land in the pocket dimension of the Vess at the same time. (AUDIO: The Light at the End)

In a different body, Straxus was sent by the High Council to the Doctor's TARDIS. He ordered the Eighth Doctor to Lonsis in 2006 to retrieve Lucie Miller from a temporal blackspot. The Doctor agreed on condition that Straxus fix his TARDIS. Straxus agreed and gave the Doctor a time ring for his mission.

On the Doctor's return from his mission, Straxus told the Doctor why Lucie was originally taken out of her own time and sent to the Doctor. Straxus then helped the Doctor defeat the Cybermen on Lonsis before returning to Gallifrey. (AUDIO: Human Resources)

Straxus was later sent by the Time Lords to take the Doctor back to Gallifrey, where he was to be quarantined with the rest of the Time Lords in order to prevent the resurrection of Morbius. (AUDIO: Sisters of the Flame) Straxus failed to find the Doctor in time and instead was captured by Cristophe Zarodnix and was forced to surrender his DNA in order to resurrect Morbius. Straxus was imprisoned for ten years while Morbius fed of Straxus' life energy whenever he became weak. The Doctor and Lucie came for Straxus and the Doctor sacrificed his life to save the universe from Morbius. Straxus' life energy was restored after the Time Lords corrected history. Straxus was taken back to Karn, where he offered to take Lucie home to Earth. (AUDIO: The Vengeance of Morbius)

In another incarnation, Straxus was sent on a mission for the Time Lords to London in 1893. He became trapped there and decided to place ancient historical treasures in a market place where they were never meant to be. By doing this he would reshape human history, which would in turn inform the Time Lords as to which time period he was trapped in. During this time, an attempt was made on his life by Septimus, one of his Cwejen clones. (AUDIO: The Adventure of the Diogenes Damsel)

Following another regeneration, Straxus was ordered by the Lord President of Gallifrey to send the Doctor to France during World War I. (AUDIO: The Great War)

Straxus later saved the Doctor and his new companion Molly O'Sullivan from a group of Daleks. His TARDIS was attacked by the Daleks and he escaped back to Gallifrey. (AUDIO: Tangled Web)

In his next incarnation, Straxus became sick of the acts that the Time Lords had commited. He was found by the Dalek time controller, who had his DNA altered and he became known as Kotris. Kotris spent centuries on the planet Srangor helping the Daleks create a Temporal Chamber. (AUDIO: X and the Daleks) Knowing that his future self would become an enemy of the Time Lords, the younger Straxus attempted to commit suicide by throwing himself off a mountain on Srangor but was prevented from doing so by a temporal drone sent by Kotris. (AUDIO: The Great War, X and the Daleks) Kotris was erased from history when his earlier self, seeing what he would become, was exterminated by the Daleks. (AUDIO: X and the Daleks)

Behind the scenes

 * On the 12 July 2011 edition of The Big Finish Podcast, Nicholas Briggs revealed that the original actor hired to play Straxus had to be fired. When the original actor proved unsuitable for the role, Briggs quickly called someone he knew — Nickolas Grace — to take over. The crew became so enamoured of his performance on the audio story Human Resources that they wrote Straxus into The Vengeance of Morbius. Briggs went on to mention that this was the only time in Big Finish's Doctor Who production where an actor had to be fired for performance deficiencies. It's unclear whether Briggs was exaggerating, but it is probably fair to say that such dismissals are at least highly unusual at Big Finish.