In AF, there are several, some of which you would never expect. These include: Opal Koboi, The Goblins, and even AF himself in two different books in the series. The most important and most seen antagonists in the novels are Opal Koboi and Beauty Smith. They are both destructive, and will do whatever they have to do to get what they want. Despite this, they still have their differences.
Beauty wants mere money, while Opal wants complete control of the world, along with revenge on the people that caused all of her worldly problems. Taking all of this into consideration, they are more like each other than not, but still have entirely different motives. Also, Opal has so many more resources at his disposal than Beauty. Beauty is pretty dumb, and acts out of anger rather than planned movement, and is far less efficient in his dealings than Opal.
I conclude that these two exceptional novels are alike, yet still have their differences. They are bothe liked by many, but Artemis Fowl is definitely more complex than White Fang, with all of its plot twists and different characters, along with the changing of the view perspective about every chapter. Though they seem like completely different books on the outside, they prove to be similar in many ways, if read with understanding of what you are looking