Willie Nelson is famous for two things: Being one of the greatest country musicians ever and being one of the greatest proponents of weed ever. Meanwhile, Gandalf the Grey is also famous for two things: Saving Middle-earth from the evil of Sauron and enjoying the halfling leaf far too much.
Not that Willie is going to make a big deal about it, of course. After all, he's far too mellow for that. But since he does feel such a strong bond with J.R.R. Tolkien's legendary wizard, Nelson did put together this impressive audition reel to show director Peter Jackson just what the red headed stranger can bring to the table.
And as for McKellen, well, as Nelson himself puts it, "He's a good actor. But hell, I'm Willie Nelson!"
Hard to argue with that.