Straxus (The Adventure of the Diogenes Damsel)

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

Biography
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. (BFA: Human Resources)

Straxus was later sent by the Time Lords to help the Doctor defeat Zarodnix and stop the resurrection of Morbius. (BFA: Sisters of the Flame, BFA: The Vengeance of Morbius)

Following a regeneration, Straxus went on a mission for the Time Lords to 19th century Earth. 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. (BFBS: The Adventure of the Diogenes Damsel)

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 BFA: 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.