Not to mention, he's also as far as I am aware, one of a very small number of villains in an animated movie to actually succeed in their plans. In most other movies, it's due to bad luck or circumstance that the villain gets what they want.
But Scar knew that he had to get rid of Simba and Mufasa, and set out to do exactly that. He didn't rely on a herd of wildebeest to conveniently run over the king, but he planned out exactly how to make sure that it will in fact happen.
In short, Scar is one of the few villains who actually did something.