Like King Pistachion and the other Pistachions, Derek is bent on world domination. He spent seven years alone brainstorming his overthrow of the humans before carrying out a plan that would take fifty years to complete. He appears to be a strong leader and is generally well respected by his kin. The plan he designed relied heavily on patience and stealth, and up until the end had been executed flawlessly.
In spite of his dedication to carrying out his father's plans, Derek took a summer off to do some modeling. He calls himself young and foolish for doing so but claims he has no regrets.
He has a habit of focusing on his own monologues to the point he becomes oblivious to the actions of his prisoners, who've escaped a number of times because of it. This is a trait that stays with him throughout all fifty years of his plan, from his first confrontation with Milo in the studio to his final attempts at converting the last of the humans.