Second Master

The Second Master is the second incarnation of the Time Lord known as the Master. Having been caught by the Time Lords in his first incarnation, he was brought back on Gallifrey and was forced to work as an Ingenieur for the Time Lords.

He created a breach which allowed Omega and his antimatter universe to try and come back into the Universe (TV: The Three Doctors). Seeing the chaos this made, he jumped on the occasion and stole an old type 40 TARDIS and flew off.

The forcefield created by the Time Lords to protect Gallifrey after Omega's try to come back caused significant damage to his body. He had to regenerate, and he became the Third Master.