George Hackenschmidt.

George Karl Julius Hackenschmidt (aka ‘Hack‘ or ‘The Russian Lion‘) was a strongman and championship wrestler in the early 1900s. He is now best remembered for a squat technique – the Hack Squat. This exercise focuses attention on the quadriceps – largely on the vastus medialis. In performing this lift in 1902 he knocked out a staggering 550 reps with 110 lb.


Technique
This is a pretty simple lift to get used to, and visually it is similar to completing a deadlift with the bar behind the back. Start with the bar elevated (using a rack, blocks or anything else adjustable) to a point about 4-6 inches below your glutes. Place a block of wood or a couple of plates on the ground in front of the rack, which will be used to elevate your heels by an inch or so.
Standing with your back to the bar, grab the bar and walk forward until your heels are on the block of wood. Keeping your back upright, and your glutes in the same vertical line, squat down by letting your knees come forward as far as possible. Once your knees have gone as far as they can, lower your hips. Reverse the process and return to the start position.
NB : Be careful not to round your shoulders, and make sure your hips are beneath your shoulders at the bottom position of the lift.
See also
EXRX (Exercise prescription)
www.exrx.net/WeightExercises/Quadriceps/BBHackSquat.html
George Hackenschmidt: The Russian Lion
www.naturalstrength.com/history/detail.asp?ArticleID=308