Sunshine was formerly a dentist, who serviced some of the most wealthy members of NCR society as he was incredibly gifted in his work. However, one day a simple cavity filling procedure became a blood bath as went completely insane with his numatic drill and brutally murdered his patient. Sunshine has since adopted this new persona, constantly painting his face yellow and black to resemble a smiley face.
Mr Sunshine is cruel and manipulative and incredibly erratic as he went from place to place. He seemingly has no goals, no desires and his objectives change all of the time on whim. However, when he's feeling charitable, he may prove useful to any cause that he is willing to put himself towards or he may just slap a 'have a happy day' sticker on your forehead and run off cackling or he might just gouge your eyes out.
It is implied by Tamannaah that Sunshine's insane clown persona is a persona of a persona. She deduced that Sunshine is trying to bury his past and his failures under a psychotic face, that people would either be too afraid of or too focused on to notice the man behind it.
He interestingly shows quite a bit of interest, both sexually and personally in Maria. Maria, being a minor, raises a number of concerns to those who observe the relationship as it develops. Though Sunshine has no qualms with indulging in child grooming, he is not specifically attracted to Maria, because she is a child. Sunshine is drawn to Maria's dark past and psychotic potential. Her being a child is inconsequential to him as his main objective is to make her his protege, eliminating all other distractions and ensuring that she is 100% dedicated to him.
Mr Sunshine appears in Brothers in Binds and Godless America. He is mentioned, numerous times, throughouot Legends of the Wastes.