Theodore Kosloff was born in Moscow, Russia and learned to dance at the Moscow Imperial Theater, graduating in 1901. In 1909 he joined the Diaghileff ballet company. Performed and acted in many movies. He had his own ballet school in Los Angeles, CA. Taught many famous personalities of the day such as Agnes de Mille, Colleen Moore, Bebe Daniels, Natacha Rambova, etc.

Theodore and Natacha had a very stormy relationship while in Europe. Kosloff shot and seriously wounded Rambova. She survived and went on to design costumes and set designs in Hollywood, where she met and married Rudolph Valentino.

Alexis Kosloff was Theodore's brother. Alexis was a very successful Ballet dancer, Dance instructor, writer and choreographer. Organized the Kosloff Dancers as well as writing many books on dance. Alexis was in the 1917 - 'The Dancer's Peril' silent film as Nicholas.

Although they did both, Theodore mainly did Movies, while his brother mainly did Stage/ Broadway performances.