Simeon Bekbulatovich (?—1616) (Sain-Bulat, Саин-Булат), by a strange quirk of Ivan the Terrible was the Veliki Kniaz (Grand Prince) of the Whole Russia, 1574-- 1576. Simeon, a scion of the Genghis Khan line, was a Khan of Kasimov tatars, Christianized.

After executing a large number of boyars, archimandrite of Chudov , and the archpriest (протопоп), Ivan IV left Moscow, humbly named himself "Ivan from Moscow" (Иван Московский, "Ivan Moskovski") and crowned Simeon for rule. Historians have a number of opinions as to why Ivan did so.

After his short "rule", Simeon was set as a ruler of Tver and Torzhok. Under Boris Godunov he fell into disfavor, and False Dmitry I banished him to a monastery as a monk.