Who was the trombone player at beginning of movie Easter Parade who Judy Garland put her arm around on band stage?

That trombone player at the beginning of "Easter Parade" was Raymond Scott, a well-known jazz musician, composer, and bandleader.

He's actually playing a distinctive trumpet solo in the scene, not trombone. He was known for his quirky and experimental music, and his unique style is clear in the solo. He and Judy Garland were both part of the Fred Astaire-Judy Garland musical pairing for the movie, and this scene features the two of them on stage with the band.