The Shadow Men are the people settled along the mountainous region of Essos known as the Shadow Lands, in the Further East of the known world. Shadow Men are known for covering their bodies in tattoos and wearing red lacquered wooden masks.
Throughout history, some Shadow Men have engaged in piracy and reaving. The maroon emperors of Yi Ti kept their court in Jinqi to better guard the borders of the empire from reavers from the Shadow Lands.
A Game of Thrones
During her stay at Vaes Dothrak to be presented to the Dosh khaleen, Daenerys Targaryen often spends her mornings in the Eastern Market, and enjoys wathcing the people there, including Shadow Men, which she considers dour and frightening.