薩摩国
was a "daimyō" (feudal lord) of Satsuma Province during Japan's Sengoku period. He was born into the Mimasaka Shimazu family (伊作島津家), which was part of the Shimazu clan, but after his father Shimazu Yoshihisa died, his mother married Shimazu Unkyu of another branch family, the Soshū (相州家). Tadayoshi thus came to represent two families within the larger Shimazu clan.