What Famous Actor of Stage & Screen?

What famous actor of stage & screen played a character largely based on Errol in a fictional Hollywood film?

Clues:

1) Not Peter O’Toole

2) Not Kevin Kline

3) He was in movies with Errol

4) His performance as the “Errol Flynn” character was very highly regarded.

5) He has at least one Grammy Award and is one of two key voices on one of the most notable songs of all time.

— Tim