David Xanatos is a man of extremes. He's extremely rich, extremely powerful, extremely arrogant. But more than that, he's extremely smart. You may hate him, but you'd be foolish not to respect him... in extreme amounts.
Xanatos is the CEO and majority stockholder in Xanatos Enterprises, an impossibly huge, international conglomerate, based in New York. X.E.'s holdings include but are not limited to: Scarab Corporation, a company which specializes in the development and manufacture of robotics; Gen-U-Tech Systems (or G-U-T-S, for short), which specializes in genetic engineering R. & D.; and Xanadu Entertainment Productions. Through X.E., Xanatos maintains tight control over many purely legitimate businesses, many that walk the line and many that are flat out illegal.
Xanatos is not a mad dictator or a war-monger. He's not out to destroy humanity, take over the world or bring our system-of government and commerce crashing to the ground. Why would he want to? His success has seen no limit under the current system.
Xanatos favorite word is "Acquire". Acquire things; acquire people; acquire power ... anything he sets his sights on. What he can get by legitimate purchase, he'll buy; it's easier. what he can't buy, he'll take... by subterfuge if possible or force if necessary. What he can't take (i.e. our gargoyles and their obedience), he might destroy, less out of spite than to make sure it won't later be used against him. But he hates waste, so he wouldn't make the latter decision lightly. in Xanatos, opinion, he acquired Manhattan long ago. It's his town.
As humans go, Xanatos is a remarkable physical specimen, over six feet tall and built like a football player or wrestler. He's trained in most every martial art you could think of, and he's proficient in all of them. But you might not notice any of that at first. He's usually impeccably dressed in custom made suits. He's not afraid to get his hands dirty, but that's usually a last resort. He's smart enough to know he couldn't conquer in a toe to toe physical confrontation with Goliath. And he has nothing to prove by trying. But he might have a lot to gain by cheating. Or by using some of the technology his companies have created to win. He's particularly fond of his new Gargoyle Battle Armor.
And he doesn't often lose. But when he does, he doesn't throw a tantrum. He's highly confident in himself and is sure he'll triumph eventually. He simply moves on to the next plan. There are always contingencies.
In some episodes, Xanatos will lead his forces personally. In others, we might not even know he was involved until an epilogue at the end reveals it. And plenty of times he'll have no involvement whatsoever. But you can bet, if something rotten is happening in New York, the odds are good that Xanatos is behind it.
Demona thinks that Xanatos is a perfect example of the worst humanity has to offer. So she's perfectly happy to use him to suit her ends. He provides technology and raw materials, weapons etc. Likewise, she has opened up a whole new world of knowledge to him (medieval creatures, magic, possibly immortality), so he's perfectly happy to use her as well. But their goals are very different, which could just as often make them enemies. If she's figured out a way to poison every human in Manhattan, Xanatos is NOT going to help her. In fact, he might strike a very temporary alliance with Goliath to stop her.
Goliath and the other gargoyles know that Xanatos is a formidable enemy, and they're learning that he can't be fought by tenth century means alone. Elisa feels particularly frustrated that she can't seem to ever stop him entirely. At the end of the pilot, she does arrest him, but for the next few episodes, he operates his empire successfully from prison. And soon enough, he's out on a reduced sentence.