DD

D.D. (short for Diamond Dog) was the wolfdog pet of the Diamond Dogs, especially their leader, Big Boss, during the 1980s. The wolfdog, like its owner, was missing its right eye, resulting in it wearing an eyepatch when it was older.

At some point, D.D., as an orphaned pup, was found by Big Boss near its dead parent, and taken to Mother Base as its new home. After Big Boss came back from a mission, Ocelot was present with the pup to greet Big Boss when he returned, with Big Boss giving it some love. A few days later, as Big Boss was preparing to leave, Ocelot had D.D. come with Big Boss, who had been trained for combat missions by the latter.

Behind the scenes
D.D. is a character from Metal Gear Solid V: The Phantom Pain. The wolfdog made its debut in the TGS 2014 demo, more specifically the showing on September 19/September 20. Like Quiet, it will accompany Snake on missions via the buddy system, and like Quiet, meeting it will be entirely optional.

Coincedentially, the Star Fox and Super Smash Bros. Brawl character Wolf O'Donnell was a wolf who wore an eyepatch, similar to D.D., although in Wolf's case, he didn't need it for a bad eye and it was on the left eye instead.