Great Royal Wife, or alternatively, Chief King's Wife, is the title that was used to refer to the principal wife of the pharaoh of Ancient Egypt, who served many official functions.
Hatshepsut was Great Royal Wife to Thutmose II, then regent for her stepson Thutmose III, before becoming pharaoh in her own right (Metropolitan Museum of Art)
The Vulture crown, a crown worn by Great Royal Wives and female pharaohs
Concubinage is an interpersonal and sexual relationship between two people in which the couple does not want to, or cannot, enter into a full marriage. Concubinage and marriage are often regarded as similar, but mutually exclusive.
Ushabti of a concubine, with a naked body, jewelry underlying the breasts, and shaved pubis with visible vulva, wearing a heavy wig with erotic implications (painted wood, 2050–1710 BC)
Statue of Yang Guifei (719–756), the favoured concubine of Emperor Tang Xuanzong of China
Portrait of a concubine, by Chinese painter Lam Qua, 1864
16th-century Samurai Toyotomi Hideyoshi with his wives and concubines