Mstislav Mstislavich the Bold (Ukrainian: Мстисла́в II Мстисла́вич Удатний, Russian: Мстисла́в Мстисла́вич Уда́тный; Удало́й) was one of the most popular and active princes of Kievan Rus' in the decades preceding the Mongol invasion of Rus'. He was the maternal grandfather of prince Leo of Galicia, who became Grand Prince of Kiev.
He was the son of Mstislav the Brave of Smolensk by a princess of Ryazan. In 1193 and 1203, his bravery in the Kypchak wars brought him fame all over Kievan Rus'. At that time, he married a daughter of Kypchak Khan Kotian. In 1209 he was mentioned as a ruler of Toropets. A year later, he came and took the Novgorodian throne, seizing Sviatoslav Vsevolodovich's men (Sviatoslav himself was detained in the archbishop's compound in Novgorod).
On his way to Novgorod, Mstislav delivered the key town of Torzhok from a siege laid to it by Vsevolod III of Vladimir. He led two successful Novgorodian campaigns against the Chudes in 1212 and 1214. In 1215, he expelled Vsevolod IV from Kiev and elevated his uncle Mstislav Romanovich to the throne.