Snake has a new best friend in Metal Gear Solid V: The Phantom Pain. And thus was Call of Duty Dog completely forgotten.
Because a scantily-clad sniper is hardly man's best friend, Snake has another A.I. companion to aid him in next year's epic adventure. Snake finds DD — short for Diamond Dog — in the woods during his journeys.
Once retrieved, DD enters the tender care of Ocelot, who trains him until he's big enough to pose dramatically with his master.

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Once properly schooled in theatrics, DD can accompany Snake or Big Boss or whatever you want to call him on missions.
What does DD do on those missions? I have no idea, but Polygon says he'll eventually wear an eye patch, which will be adorable beyond words.
See? Eye patch!
DISCUSSION
So first there was the sniper with revealing clothes and now there is a wolf...oh Kojima, you symbolic little rascal