Big Mouth () (c. 1822—October 29, 1869) was an Oglala-born leader of the Brulé Lakota, regarded by the Brulé for his bravery and aggressive military leadership. He was one of the signers of the second Treaty of Fort Laramie in 1868 and remained a bitter opponent of further American settlement, ridiculing Spotted Tail and other Sioux leaders upon their return from a mission to Washington, D.C.. He was the first son of Old Chief Smoke (1774–1864) and his third wife, Burnt Her Woman. His twin brother was Blue Horse.