Nikolai Grigoryevich Rubinstein (Russian: Николай Григорьевич Рубинштейн; 14 June [O.S. 2 June] 1835 – 23 March [O.S. 11 March] 1881) was a Russian pianist, conductor, and composer. He was the younger brother of Anton Rubinstein and a close friend of Pyotr Ilyich Tchaikovsky.