The Felboar from Warcraft III.
Felboars are hostile level 67-68 demonic helboars found in Shadowmoon Valley.
Felboars have black spikes jutting from their back, but otherwise look a lot like the standard helboar. They can go into frenzy, and when they do, they grow, turn red, and deal increased damage.
Oronok Torn-heart has managed to domesticate a few to help him farm for tubers.