Sylvester McCoy (Doctor Who) has already been cast as Radagast the Brown, though last I heard he hadn't officially signed any contract. That was during the whole labor issue in New Zealand, though. Now that that's been sorted out, McCoy will probably sign on officially.
Uh oh.
A white, elderly, English Dr. Who actor playing a character called "Radagast the BROWN".
That'll get the PC nutjobs' heads spinning in "Exorcist"-like rage!!!