Percussionist hero accompanying Romeo (5)
I believe the answer is:
starr
'percussionist' is the definition.
(Ringo Starr, drummer from The Beatles)
'hero accompanying romeo' is the wordplay.
'hero' becomes 'star' (as in the star of a film).
'accompanying' means one lot of letters go next to another.
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'star'+'r'='STARR'
(Other definitions for starr that I've seen before include "Beatle Ringo" , "Freddie . . . . . Ate My Hamster" , "English rock star and drummer, b. 1940" , "Ringo - (The Beatles)" , "Ringo --, drummer" .)