Nobel Prize "for the discovery of the called asintotic freedom in the strong interaction theory".
Only four types of fundamental forces are the ones governing the universe: the gravitational, the electromagnetic, the called weak force (responsible for the spontaneous breaking of certain atomic nucleus and their radioactivity) and the strong force.
This strong force is the one joining the smallest particles of matter known: the quarks. Wilczek explained, being just 21 years old, how this force worked, which, moreover, works in a surprising and anti-intuitive way: the closer are the quarks, the lesser force they exert among themselves. That is, when they are very close they feel almost free and they do not feel the effect of the others.
This discovery was the key for the development of one of the basic branches of Physics: the quantum chromodynamics. Wilczek is also a renowned writer in North American scientific magazines.