Mask of Death

Gives melee Heroes a vampiric attack that converts 50% of their attack damage into life.

This horrific ebony mask is carved in the likeness of a demon's face. Tremendous curved horns sweep up and back out the forehead and around behind the ears, while the fangs seem to glisten as if ready to bite into living flesh. When worn, the eye sockets become covered with a glassy shield that seems to glow red to any observers. When the wearer speaks, their voice utters forth like a guttural growl.

Source
Thrall and Cairne Bloodhoof can find one in By Demons Be Driven, chapter 8 of the Warcraft III orc campaign, The Invasion of Kalimdor.

Illidan can find one in The Brothers Stormrage, chapter 8 of the Frozen Throne sentinels campaign, Terror of the Tides.

Illidan, Kael, Lady Vashj and Akama can find one in Lord of Outland, chapter 6 of the alliance campaign, Curse of the Blood Elves.