>>106448304He is the opposite of the Doctor. While the Doctor helps, the Master loves to troll/fuck things up sometimes humanity itself, sometimes the Doctor, or both at the same time. The Master also desires conquest as well. He wants power and will take it.
In actuality, he was pretty consistent from the 70s to 80s.
https://www.youtube.com/watch?v=g10uWQ7zsXM