Leopold Auer
Keller was born in Delphos, Kansas, and began his violin studies at Bethany College in Lindsborg, Kansas, graduating in 1907. From 1907 to 1911, he continued his studies at the Stern Conservatory in Berlin, Germany. Keller also studied with Anton Witek in Prague (1912) and Leopold Auer in St. Petersburg, Russia (1913 to 1914).