Sutpen's ambition (referred to as his "design") drives the entire story of Absalom, Absalom!. His formative experience at the door of a white man's mansion changes the direction of his life. And from that point on, Sutpen is determined to have a big estate, money, and unrivaled power. But Sutpen's greatest strength is also his greatest weakness (great for job interviews!): he will let nothing stop him from building Sutpen's Hundred according to his vision, even if that means buying slaves, abandoning his wife and child, and repudiating his wife. In the end, Sutpen's ambition isn't realized because it's flawed: his inhumanity in the face of his ambition is what kills him in the end.
Sutpen's ambition grows out of the naïve belief that people can completely recreate their lives. He fails to consider that some people do not want to be puppets in the service of someone else's plan.
Other characters in the novel are just as ambitious as Sutpen, but they just aren't as amoral or resourceful.