Well, Every pokemon. Just like humans have natures. A nature is the personality of a pokemon, As you probably know, some pokemon are good in one stat and bad in another. So you want to focus on their good stat. This is where natures come into play, Natures make one stat be less then it would normally be, and another stat more then what it would normally be. Such as the "Adamant" nature, gives you higher attack, but lower Sp.Atk. This is wanted on pokemon like Electivire, with mostly attacking moves. I found A list of what every nature does, and I will include it below. If you are generally unsure, check on Smogon to find the best natures.