Feyd-Rautha Harkonnen is the nephew of the Baron Harkonnen. He is the same age as Paul, and he's also a skilled fighter. Learning from his uncle's example, Feyd is power hungry, desiring the position of baron and later plotting with his uncle for the Imperium throne.
No, not that Dark Knight—though a Batman cameo would have been cool. We mean that Feyd-Rautha encompasses the dark knight archetype. Dark knights are tremendous warriors, but unlike noble or white knights, they use their skills and swords to benefit their own goals and ends. Helping other people? Nobility and honor? That noise is for chumps and losers.
We can see this side of Feyd-Rautha in almost ever scene he's in. He kills a gladiator in the arena to gain popularity among the people of Geidi Prime. He aligns himself with Hawat in an attempt to have the Baron assassinated. He only duels Paul because "[h]e could see a way to power opening before him [as] the Emperor surely would reward whoever killed this troublesome duke" (48.267). Not an ounce of him cares that his uncle, his cousin, and the entire army were wiped out a few moments ago. For Feyd-Rautha, only the acquisition of power matters. His uncle taught him well. We guess.