Duke Theodore Rostislavich nicknamed Theodore the Black (b. in about 1230s – d. 1298), Феодор Ростиславич Черный in Russian, is a saint of the Russian Orthodox Church and was a ruler of Smolensk and Yaroslavl. His father Prince Rostislav died in 1240. Theodore was Duke of Mozhaysk from his youth. In 1260 Theodore married Maria Vasilievna, daughter of Prince Basil of Yaroslavl. Theodore then also became prince of Yaroslavl. Maria soon died, and their son Michael was raised by his grandmother, princess Xenia. Theodore himself went to Sarai, the capital of the Golden Horde. He married the daughter of the Khan Mengu-Timur. She was baptized and received the name Anna. Theodore and Anna had two sons, David and Constantine. In 1290 when he learnt that his first son Michael was dead, Theodore returned to Yaroslavl.
In alliance with the Mongols, he was a prominent figure of the politics in middle Russia.