Constable Cooper is supposedly the "Dark Side" of Sly Cooper. He is a strict law-abiding fellow, and has completely forgotten about his family's legacy. Interestingly enough, however, he remembers all of his ancestors' techniques, including his father's Laser Slide.
When Sly Cooper lost his memory, it was initially believed that Sly had faked his loss of memory to get closer to Carmelita Fox. However, this was quite the opposite; Sly had legitimately lost his memory, and through the training of Carmelita and her police force, he slowly but easily turned into Constable Cooper, as dubbed by Carmelita soon after Sly's battle with Dr. M.
Constable Cooper is a very black-and-white officer, who does not pardon any criminal, regardless of the severity of their crime. This may also be because he has lost a great majority, if not all, of his past memories. It is quite apparent that Cooper is a strict officer when he first encounters Bentley and Murray entering Interpol HQ in Venice.
Cooper's only soft spot is for Carmelita. When Bentley attempted to convince Carmelita that Sly needed to go back in time to relearn his ancestry, Cooper instantly stepped in, and almost severely injured Bentley had Carmelita not recognized Cooper's limits.