The 501st Legion, also known as the 501st Battalion during the Clone Wars and later known as "Vader's Fist" and the Five Hundred and First, was an elite unit of clone troopers commissioned by Supreme Chancellor Palpatine during the Clone Wars that later became a stormtrooper unit. Made up of units like Torrent Company, the 501st fought in many battles, such as the Battle of Teth and the Battle of Coruscant, becoming one of the most well-known legions. In 19 BBY, the 501st became Darth Vader's personal unit as he led them during Operation: Knightfall, in which the clones helped take down the Jedi, whom they believed to be traitors to the Republic.
By Tanathiel Deviant Art.
lol looks like Darth Maul on steroids.
Maul's not a Twilek, he's a Zarbak. (I hope my spelling is right I've stopped checking the Star Wars wiki for correct spelling)
I did type "looks like", I knew it was a Twilek when I first saw it, I was just poking a little fun into a serious looking picture.
*Zabrak
(I actually remembered after 100 times of checking!)