Billy Strayhorn, originally hired as a lyricist, began his association with Ellington in 1939. Nicknamed "Swee' Pea" for his mild manner, Strayhorn soon became a vital member of the Ellington organization. Ellington showed great fondness for Strayhorn and never failed to speak glowingly of the man and their collaborative working relationship, "my right arm, my left arm, all the eyes in the back of my head, my brain waves in his head, and his in mine". Strayhorn, with his training in classical music, not only contributed his original lyrics and music, but also arranged and polished many of Ellington's works, becoming a second Ellington or "Duke's doppelganger". It was not uncommon for Strayhorn to fill in for Duke, whether in conducting or rehearsing the band, playing the piano, on stage, and in the recording studio. The decade ended with a very successful European tour in 1939 just as World War II loomed in Europe.