Dmitri Mendeleev

[via: nndb.com]
Dmitri Mendeleev, founder of the Periodic table.
Dude, whatever. He looks straight up homeless.
I wouldn't mess with him though, that is a pretty badass beard.

Bernhard Riemann

[via: Simithsonian Institution Libraries]

Bernhard Riemann, a great German Mathematician contributed to differential geometry and even helped pave the way for development of general relativity. As for the beard, it is just incredible. Full and dignifited. 

Leonardo Da Vinci

[VIA: paradoxplace]
Leonardo DaVinci a scientist, mathematician, engineer, inventor, anatomist, painter, sculptor, architect, botanist, and writer.
Whew.
DaVinci is a all around badass, with a badass beard.

Charles Darwin

[VIA: goecuador]
The key to Darwin's successful scientific career? The Beard, duh. It really has perfect dimensions to classify him as a serious scientist: long, white, and just mismanaged enough to add a hint of eccentricity.