Here is my short list. Not simply a measure of raw talent but also his/her contribution to the sport. Modern freestyle skiing would not be what it is today without these folks.
Stein Eriksen - famous racer often credited for developing "aerial" skiing
Eddie Ferguson - 70s Hot Dog legend
Wayne Wong - an absolute legend with too many accomplishments to list
Jonny Moseley - introduced new freestyle maneuvers to mogul skiing in the late 90s and is credited as one of the pioneers of "newschool" skiing
Mike Douglas - credited with developing the first twin tip ski
Jon Olsson - Swedish ski racer who invented a number of new double flips in the late 90s and early 2000s.
Candide Thovex - IMO probably the single greatest skier of all time
Tom Wallisch - took newschool skiing to a new level with his highly technical rail maneuvers
Henrik Harlaut - the modern face of freeskiing. Henrik introduced the world to nose butter triple flips and is one of the best all around skiers in the world
Who are your favorite freestyle skiers and what have they contributed to modern freeskiing? Post pics and vids to backup your claim! Hopefully this thread will allow us to bridge the gap between different generations of freeskiers and get a real conversation started on this subject.