The Second Known Master (Peter Pratt and Geoffrey Beevers)
http://www.youtube.com/watch?v=awxHDUfzOg0 But you cant keep a bad man down. He returned in the Fourth Doctor story The Deadly Assassin. Now at the end of the his regeneration cycle, this Master was a twisted, mangled creature, almost unrecognizable as anything even remotely human. This was the beef jerky in a cloak Master, and his mind was now as twisted as his body. For this version of the Master, the all-consuming desire was to get a new body and/or a new set of regenerations. To that end, he committed all manner of atrocities and, in the second-to-last Fourth Doctor story, succeeded in his goals by stealing the body of a kindly man named Tremas. Now resembling something more human, and played by Anthony Ainley, this version of the Master went on, shortly thereafter, to drop the Doctor from a radio telescope, causing him to regenerate. As a side note, the beef jerky Master has begun appearing in audio stories from Big Finish, most notably
alongside Tom Baker as the Fourth Doctor. These are great, and well-worth picking up.