Dean is basically a rich white guy. He's really sassy, and has a good cold shoulder.
He's most certainly a slytherin.
He's very cunning, and never second guesses his decisions or opinions.
That said, he's not always stubborn either though. If someone gives him a good point, or he finds a more intelligent answer to something, he'll be swayed.
He doesn't have a lot of friends. He tends to keep to himself, and take care of his immobilized sister.
His sister was kidnapped and held for ransom by some criminals, and when they got her back she had such bad PTSD and whatnot that she was badly shellshocked to the point of not talking, or moving (like a soldier from WW1 & 2). However, in the court room, the criminals were not put away for as long as they should have, and were essentially written off.
Dean vowed to never let another criminal get away with that sort of thing again and became a lawyer.
This event also destroyed his relationship with his parents. His parents are (and were) never around due to business and travel, and eventually when Dean was old enough, they also moved out to Europe semi-permanently. Dean took possession of his sister legally as soon as legally possible, and has since bought his own house, and moved his butler and maids to his own place.
He went to the same law school as Robert, where they were friends at first, but since they have started to work together they have found that they don't get along well. It's not because their personalities or whatever collide, but rather their methods of work.
Dean is ruthless in the courtroom, whereas Robert takes an intelligent and persuasive approach. They both have served well to their bureau, and have a good case record. They also share a paralegal.

Reupload from dA