Creole doesn't appear until the very end of the story, and we don't really get to know that much about him. Nevertheless, he's a pretty important figure. Creole is the one who welcomes Sonny back to the jazz world, who guides him (and us) through his first performance after being arrested, and who makes Sonny feel comfortable enough to finally let go and lose himself in his music.
Creole sort of bridges the gap between Sonny's and the narrator's worlds. Although he is most definitely a musician and lives (literally and figuratively) in Sonny's world, he also has the experience that Sonny does not. He's like another father figure to Sonny, and this makes him a bit like the narrator. But Creole has a certain wisdom that neither Sonny nor the narrator does, so he's really a teacher to both of them and to us as readers. It's Creole who leads us through the performance in the club, and in this respect we think he's a pretty awesome guide.