Rick Rubin has one of the most formidable beards in rock, and age has only made it more impressive. When he was younger, he looked a bit like Hagrid from Harry Potter, but these days, it's more of a Gandalf the Grey look.

Anthrax guitarist Scott Ian has been cultivating a distinct beard style for a few decades now – a thick stalk of dark hair jutting from his jaw, while the rest of his face and head is clean shaven.

Kings of Leon frontman Caleb Followill has a fairly modest beard, but it's a big part of his character – one look at the dude and you get a good sense of his booze-loving, Southern rock spirit.

My Morning Jacket main man Jim James has a great big mop of hair that's complemented by an old-school rock beard. It's a look that could be intimidating on some, but it brings out a sweet, gentle quality in his face.

Black Keys rocker Dan Auerbach keeps his beard short and tight, roughly echoing the ethos of his band's music. Scruffy, but under control.

Jim Morrison is best remembered for his early, clean-shaven look, but many Doors fans prefer the singer as he developed into a sort of hairy, Dionysian rock shaman.

Dave Grohl's beard brings out a sweet everyman quality in his face – despite all his success with Nirvana and the Foo Fighters, he just always looks like a regular dude.

The Grateful Dead had a lot of great iconography, but even their dancing bears have nothing on Jerry Garcia's famous beard, which encased much of his face like a big brown shrub.

All of the Beatles had beards in the second half of their career, but George Harrison stuck with the look much longer than his bandmates, making it a defining part of his physical appearance. It suited him well, highlighting his mellow charm and spirituality.

ZZ Top is pretty much the ultimate in rock beards, but even in that crew, Billy Gibbons' astonishingly long beard stands out. Beards may come in and out of fashion, but Gibbons has stuck with his look for decades, lending his band a visual flair on par with their guitar chops.