Vladimir Harkonnen is the Baron of Geidi Prime. At first, he wants nothing more than to spring Duke Leto off his mortal coil, but afterward, he sets his sights toward securing the Imperium throne for his nephew, Feyd-Rautha.
We'd like to go into depth on the Baron Vladimir Harkonnen's characterization: why he hates Duke Leto, what led him to a life of villainy, how he manages to add Feng Shui to a room with those suspensors. But we can't.
Why? Because the Baron is a villain through and through. We learn almost nothing about him except that he's a bad guy. With that said, the Baron must know he's the antagonist of the story, because he plays the role with such zeal and relish. It's like he looked at his job and thought, "Well, if you can't get the role you want, love the role you get."
The Baron is a political villain. He has his minions do his dirty work for him, so he can safely say his hands are clean should the authorities ever come a-knocking. Here are a couple of examples of the Baron trying to one-up every Bond villain ever:
And those are the just the ones off the top of our head. There are way, way more.
Time for the tricky subject. Baron Harkonnen has a sexual appetite for young boys. So not only is he the only homosexual character in the novel, he's also a pedophile, and most of the time his sexual conquests come in the form of sex slaves. So… yeah.
How should we interpret this aspect of the Baron's character? Frankly, your guess is as good as ours. It's ambiguous. It could be that the novel is trying to make the Baron Duke Leto's opposite in every way. It's possible that the novel is suggesting a moral alignment for homosexuality. It's even thinkable that the Baron's sexual appetite is another way for the Baron to dominate his enemies. In one scene, the Baron specifically wants the sex slave that "looks so much like the young Paul Atreides" (22.205). Perhaps all of the Baron's sexual conquests are his way of imagining his complete dominance over those he hates, like Paul.
As we said, it's super ambiguous, but it's also a super important aspect of the character. How you read this will really depend on how you come to view the Baron Harkonnen.