1. He's a crazy cat Time Lord. He sulked for weeks when the Doctor said he couldn't keep even one of the kittens in the 1969 incident. Martha had to stage an intervention to see Thomas Brannigan's kittens.
2. He totally stole the Brigadier for several adventures just to prove a point to the Doctor, which he promptly forgot after the first trip. The Brigadier was not pleased, as he ended up having to keep the Master from summoning Things That Should Not Be Summoned, help him escape from goo monsters, and broke his arm when the Master's TARDIS got too rowdy. However, he looked after the Master and took out most of his frustrations on the Doctor when he got back.
3. Sutekh totally went after the Master instead of the Doctor for mind control. He was very shaken up after that, and guilty for what Sutekh had made him do to the Doctor.
4. Sarah Jane once cornered him and forced him to tell all the juicy details of his relationship with the Doctor. He refuses to tell even the Doctor what she did to get this information out of him, but he has a healthy fear of Sarah Jane in the rest of his regenerations.
5. The Master was totally behind the events of Planet of the Giants. In fact, this goes for non-alt Master as well. IT WAS ALL HIS FAULT. And the cat was totally spying on them at his behest.
Alt Master
2. He totally stole the Brigadier for several adventures just to prove a point to the Doctor, which he promptly forgot after the first trip. The Brigadier was not pleased, as he ended up having to keep the Master from summoning Things That Should Not Be Summoned, help him escape from goo monsters, and broke his arm when the Master's TARDIS got too rowdy. However, he looked after the Master and took out most of his frustrations on the Doctor when he got back.
3. Sutekh totally went after the Master instead of the Doctor for mind control. He was very shaken up after that, and guilty for what Sutekh had made him do to the Doctor.
4. Sarah Jane once cornered him and forced him to tell all the juicy details of his relationship with the Doctor. He refuses to tell even the Doctor what she did to get this information out of him, but he has a healthy fear of Sarah Jane in the rest of his regenerations.
5. The Master was totally behind the events of Planet of the Giants. In fact, this goes for non-alt Master as well. IT WAS ALL HIS FAULT. And the cat was totally spying on them at his behest.