Who's Brook supposed to be in this image? In this image, we can see:


Luffy as Captain America
Robin as Agent Maria Hill
Frankie as Iron Man
Nami as Black Widow 
Chopper as Hulk
Sanji as Nick Fury
Zoro as Thor
Usopp as Hawkeye


But, I don't know who Brook should be...
Just found out who he should be!

It's Agent Phillip "Phil" Coulson being pierced by Loki

https://www.youtube.com/watch?v=-vK0FPtYTvY#t=16