First Appearance: Shadowmasters #1 (October 1989).
Appearances: Shadowmasters #1-4, issues of the Punisher that I don't have.
The Shadowmasters were a group of warriors from the Japanese province of Iga. Their origins are unknown; Japanese legend states that they were half human and half demon, and that they possessed mystic powers.
For many centuries they served as protectors of Iga Province and its people in times of strife in Iga Province and Japan. Over the long years, however, their numbers dwindled, until the Tengu was the last. The Tengu was drawn into battle with a group of renegade Japanese soldiers, with whom he had a long-running feud. The Tengu's child, and the two children of the Tengu's American friend and ally, became Shadowmasters after their fathers died, in 1972. In the modern day they finally defeated the renegade soldiers, who had formed a criminal organisation, with the help of the Punisher and the Black Widow.
Their current whereabouts are unknown.