Ellington called his style and sound "American Music" rather than jazz, and liked to describe those who impressed him as "beyond category", including many of the musicians who served with his orchestra, some of whom were themselves considered among the giants of jazz and remained with Ellington's orchestra for decades. While many were noteworthy in their own right, it was Ellington that melded them into one of the most well-known orchestral units in the history of jazz. He often composed specifically for the style and skills of these individuals, such as "Jeep's Blues" for Johnny Hodges, "Concerto for Cootie" ("Do Nothing Till You Hear from Me") for Cootie Williams and "The Mooche" for Tricky Sam Nanton. He also recorded songs written by his bandsmen, such as Juan Tizol's "Caravan" and "Perdido" which brought the "Spanish Tinge" to big-band jazz. After 1941, he frequently collaborated with composer-arranger Billy Strayhorn, who he called his alter-ego.