I have no hard and fast numbers on this but I believe most jazz musicians do not think of themselves as mentors. You want to learn? You sit in. Maybe you'll pick up some good habits. (Some very bad ones, too.) You learned from the masters by listening to and playing with. Clark Terry was different. The first line of his Times obituary used the words "popular," "influential," and "jazz education." (Miles Davis's obit had "elusive touchstone.") His mission was to have fun, play with everyone, and teach anyone who crossed his path. Even Miles. He worked with them all, Ellington and Basie, Mingus and Monk. He played for Johnny Carson and jingle-writers. When he was a child, he fashioned a horn out of junkyard metals, and the neighbors were either so impressed or so appalled that they took up a collection and bought him a trumpet. He paid that kindness forward for the rest of his life, writing jazz instruction books, teaching clinics and college, advising jazz institutes and taking kids under his wing to gently usher them into the jazz life. He lived a nice long jazz life himself. Clark Terry was 94. 

--Amelia