A good adventure tale needs a lot of things: a hero or two or three or four, a problem for them to solve, long odds, improbably escapes from certain doom, high stakes if they fail...and a Villain. It's often said that a tale of adventure succeeds as much on the strength of its villains as it does on the strength of its heroes. A great villain is fun to watch, and on some small level, we might even find ourselves rooting for him or her...maybe not for ultimate victory, but at least for keeping things tough and interesting for our hero.
The best villains are, obviously, people. Except for the ones that aren't. How's that for hedging your bets! But it's really true. When I think of adventure movies or books that I love the most, those are the ones that often boast the best villains. And in adventure tales that fall short for me, it's equally often because the villains just aren't interesting, or fun, or they are so evil and despicable that it becomes depressing just to watch them in action.
A good example of the last kind are the Gary Oldman character in the Harrison Ford-as-President flick Air Force One. At first he's OK, but as the film goes on, Oldman doesn't play him as a person who is having the least amount of fun – a villain should seem to enjoy him or herself a little – and then there's an awful scene where he threatens to kill a defenseless woman if the President doesn't surrender. The President doesn't surrender, so he kills the woman after counting down from ten with his gun pressed to her temple. The scene cast a huge pall over the rest of the movie. There was no particular thrill when President Indiana Jones defeated Oldman in the end; it was just, "OK, that monster's gone now."
Another such example is the Jeremy Brett character in The Patriot, the Mel Gibson Revolutionary War epic. Brett plays this guy as a lunatic who is perfectly happy to kill anyone he wants, and this culminates in a staggering scene of awfulness when he has his men round up an entire town's people into a church...and then bars the doors and sets the church on fire. Ye Gods. (It doesn't help that the Nazis would do just that, 180 years later.) Again, it's so over-the-top and awful that for me, Brett's final defeat in the movie had little feel of actual triumph.
So, who are the good villains, then? Well, they're all going to kill...but they make choices about when to do it, and they only do it when they must. Kind of like heroes, right? Which is why it's best if the hero and the villain can be shown to have some of the same kind of personality. I think of that wonderful scene in Raiders of the Lost Ark, when Belloq points out to Indy that they really aren't terribly different. "It wouldn't take much to make you like me," Belloq says. "To push you out of the light." And he's right. Belloq is a big reason why Raiders is the best Indiana Jones film.
Villains have to be motivated, and they have to act in ways that are consistent with their motivation. But villains also should, if they are to be compelling and believable, clearly see themselves as the heroes and the hero as their personal villain. The best example of this I can think of is Hans Gruber from Die Hard; he gets nearly as much screen time as John McClane, and it's not all just Hans killing hostages and saying evil-sounding things in his lair. Gruber's got a plan and he's got motivations, and the film lets us see his annoyance and irritation – as well as his intelligence – when things happen that derail the perfect execution of his plan. Alan Rickman lets us see Hans's wheels turning. Hans Gruber is one of the best villains of all time.
Of course, there are outliers to the above. HAL-9000 of 2001: A Space Odyssey is a fascinating villain and deeply memorable, even though his motivations are inexplicable. We're never told (in 2001, anyway) why the ship's computer would become psychotic; it's effective because of how odd a thing it is. And then there's The Lord of the Rings, whose main villain is never directly interacted with, and whose physical embodiment is a giant flaming eyeball. Tolkien's skill is such that he still manages to create with Sauron a palpable feeling of menace, and a sense that Sauron's actions are driving everything that happens in our story.
And then there are the villains in comics. Each major superhero seems to have one or two iconic villains that they tend to be the ones to square off against: Spiderman has the Green Goblin and Dr. Octopus; Superman has Lex Luthor; Batman has the Riddler, and so forth. You don't see very often things like the X-Men squaring off against the Lizard, or Batman having to deal with Brainiac (but you do see it from time to time). That's always interested me...it always felt a little bit wrong when there would be 'crossovers of villainy'. And sometimes it gets a bit hard to swallow, such as the issue of Spiderman that acknowledged that 9-11 had happened; in that issue we saw Doctor Doom shedding tears. That was just tough to believe.
Books, of course, can get even deeper with the villains. In Guy Gavriel Kay's Tigana, Brandin is portrayed at first as an evil enough man to have erased an entire nation from memory, but it quickly becomes more complicated than that, and GGK allows us to see him as a man who deeply loves his wife. I have a friend who is watching the Games of Thrones teevee series, but he hasn't read the books, so when he said, "Wow, I hope they kill Jaime this season. That guy's a scum!" I had to laugh. Is Jaime a villain? He is in the first two books. In the next two...it gets complicated.
So: villains have to be motivated, and they have to seem that they are the protagonists in their story. And they should be the tiniest little bit sympathetic. You know, kind of like this guy: