Simeon Bekbulatovich ( ; born Sain-Bulat, ; died 5 January 1616) was a baptized khan of the Khanate of Qasim. During the Oprichnina period, by a strange whim of Ivan the Terrible, he was named the Grand Prince and Tsar of the Whole Russia (1574–1576). He participated in Livonian war as a commander of the Qasim cavalry.

In 1574, after executing a large number of boyars and archimandrite of Chudov Monastery, Ivan IV left Moscow for his palace in Alexandrov. At that time he wished to be styled merely "Ivan from Moscow" and had Simeon crowned the sovereign of Russia instead of himself. Historians have a number of opinions as to why Ivan did this.

After his short and ephemeral "rule" in the Moscow Kremlin, Simeon was married to Ivan's cousin and proclaimed a kniaz of Tver and Torzhok. When Boris Godunov was elected Tsar in 1598, he viewed the former puppet monarch with suspicion and sent him away from the court. False Dmitry I, who had even more reasons to fear Simeon, banished him to the Kirillo-Belozersky Monastery as a monk.

Simeon Bekbulatovich died in 1616, when the Romanov dynasty was firmly installed in the Kremlin, and was buried in the Simonov Monastery in Moscow. Russian genealogists debate whether he left any male issue by his marriage to Ivan the Terrible's cousin. If he did, their progeny would have been the only living descendants of Ivan the Great and his wife Sophia Paleologue and, as such, should have been viewed as potential claimants to the Russian crown.