| Dr. M is the central antagonist in Sly 3: Honor Among Thieves. Dr. M is an anthropomorphic mandrill who has tried to breach the defenses of the Cooper Vault on Kaine Island for years. However, the Vault has proved impenetrable, leading him to construct an enormous fortress around it. With his sinister genius, Dr. M has created all manner of defenses, including a force of mutant beasts. Dr. M has a large amount of knowledge on the Cooper family. This stems from the fact that Dr. M filled the role of Bentley in Sly's father's gang, rather like McSweeny filled that of Murray.
When Sly Cooper and the Cooper Gang arrived on Kaine Island, they attempted to get past Dr. M's defenses to reach the vault. Unfortunately, his intellect proved too much for them, and they not only failed to open the vault, but also lost the Cooper cane. The Guru and Dimitri both attempted to recover it, but Dr. M was able to retrieve it using a mutated sea creature. Later, when Penelope eliminated his air defenses, Dr. M took control of a giant whale-dragonfly hybrid to attack Sly. He revealed his history to Sly, and seemingly lost the cane. In reality, he had attached a tracking device to it, allowing him to track Sly's movements through the vault. Going after him, Dr. M had a brief confrontation with Murray and Bentley, where he suffered defeat.
Dr. M later engages Sly in a final battle, with Sly beating him to the edge of defeat. Sly then tries to convince him that not all Coopers are bad, giving him an example on how he and Bentley's relationship works. Dr. M is confused as Sly's father was "never much of a good friend." Sly then says that all Coopers are different even if they have the same bloodline. Dr. M refuses to believe this is all true and at that time Carmelita jumps in through the window (which was another way into the vault). Seeing how Sly and Carmelita are towards each other, Dr. M then takes a shot at Carmelita Fox, only for Sly to take it and for Carmelita to finish him. Later, as the Cooper Vault collapses, Dr. M refuses to leave, and thus is crushed by falling stones. Unwittingly, he facilitated Sly's relationship with Carmelita, allowing his enemy to fake amnesia.
While originally a member of the first Cooper Gang, Dr. M felt that he was little more than a sidekick to Sly's father. Turning his back on his former teammates, he sought to steal the Cooper fortune for himself. It is quite possible, but unconfirmed, that Dr. M may have betrayed Sly's father to Clockwerk and the rest of the Fiendish Five out of spite. From this, it can be assumed that the prior Cooper Gang did not have the bonds of brotherhood that connect Sly's gang.
It is implied that Dr. M had performed some of his gene-splicing experiments on himself to become stronger - possibly using McSweeny's DNA - as he was easily able to grapple with Murray without showing signs of weakening. He has also survived damage capable of defeating even the strongest enemy, repeatedly, without slowing down or even showing the slightest signs of fatigue. He has been repeatedly zapped by Carmelita's Shock Pistol, bashed many times by Sly's cane, held into the air to receive many thousand bolts of electricity, and still manages to give Sly a concussion. He also had a computer interface built into his skull. This device, visible on his head as resembling a giant plug, allowed him to hook up to various weaponry. Among these are the largest specimens of his mutant creatures, which include:
Mutant Primate: A giant creature that Dr. M controlled while attempting to kill Sly, it also engaged Carmelita and Lt. Gronk's mercenaries in battle. It was last seen drifting out to sea on an Interpol boat with Carmelita, who presumably defeated it.
Mutant Fish: One of Dr. M's sea creatures, it possesses an appearance similar to that of an anglerfish. Equipped with explosive starfish-like disks, laser web generators, tentacles, and suction force, it was defeated after a fight with Dimitri.
Whale Fly: Created from a fusion of a whale, a dragonfly, and multiple machine parts, the Whale Fly was equipped with missiles and energy field emitters. Sly was able to defeat it using the Cooper Gang biplane.
Dr. M's final weapon, which he used during his showdown with Sly and Carmelita, was a module that attached to the top of his head. Equipped with several spider-like legs, it also had a built in propeller that allowed Dr. M to fly. Other features included a missile launcher and a generator which could produce either electricity, fire, or water as attacks. Balls of all three could be released, and Dr. M could also slide across the ground to leave a trail of them. Another of his attacks involved leaping into the air and slamming down on the ground, sending out a ring of energy. When hooked up to a slide laser emitter in the Cooper Vault Inner Sanctum, the module allowed Dr. M to fire a powerful laser beam while protected by a force field. After his battle with Sly, it appears Sly has broken all but two of the spider-like legs off. After Carmelita shows up and engages in a ranged battle with Dr. M, she destroys the remaining legs, thus causing him to topple over. He is voiced by Rick May.