The first thing you notice when you get on Willie Nelson's tour bus is a pungent aroma. Parked outside a gigantic casino and performance venue in Thackerville, Okla., Nelson offers NPR's David Greene a joint, which Greene declines. Nelson says he understands.

Vijay Iyer is probably best known as a pianist and bandleader in the African-American creative improvisational tradition — most say "jazz" for short — though he's also several other things in music. He's a composer of chamber, large-ensemble and mixed-media works; a Harvard professor; a student of Indian classical music; a father and New York City resident. Committed as he is to multiplicity, there's one place where you can see many of his interests distilled at once: in the trio he's led for nearly a dozen years.

Is there a modern-day equivalent to Duke Ellington? Or Ornette Coleman?

Who are the people today who think differently about jazz — who have created new forms, and expanded the musical vocabulary?

For 30 years, saxophonist Steve Coleman has been pushing the music forward, traveling the world to collect new sounds, rhythms and ideas. Along the way he's mentored many of the most exciting younger artists in jazz — musicians like Ambrose Akinmusire, Jason Moran and Vijay Iyer.

Benjamin Clementine's haunting voice and songwriting made him a star on Spotify after a single television appearance on BBC Two. These days, he's headlining sold-out shows in Europe. He recently signed with Capitol Records, and his first American EP, I Dream, I Smile, I Walk, I Cry, is out now.

Clementine's recent fame comes after years of busking on the streets of Paris and, before that, a challenging upbringing he still has trouble discussing. Now, the 26-year-old prefers to focus on what makes him fortunate.