Black Dire Worg

There are 2 tameable creatures with this look.

Black Dire Worg
Can Be Tamed
Fields of the Eternal Hunt, Halls of Valor (Dungeon)
Available to Horde Hunters Only
120Dunwald Ruins, Twilight Highlands (Vulpera Allied Race Recruitment Phase)
This black worg only seems to be available during the Vulpera Allied Race recruitment questline which means it's only ever available to Horde hunters, and possibly only once ever on your account. See Wowhead's Vulpera Allied Race Guide for more information on how to unlock this race.