Sometimes characters are classics for a reason. The Master has been causing trouble on Doctor Who since the late 1960s, so he must be doing something right. He serves as a campy thorn in the Doctor's side, and although many of his plans have larger implications, a lot of them seem specifically designed to irritate the Doctor. He may be trying to destroy/enslave/take over the world, but at least he's have a little bit of fun with it, credit where credit's due. Most of the time he doesn't come off as a serious threat, just a goofy little guy whose nefarious schemes are forever doomed to failure. But every once in a while, he's capable of some seriously menacing behavior. Just as the Doctor has changed form several times over the years, the Master has likewise been played by a variety of different actors, each contributing something new and interesting to the role.