Who is this Gary Gygax dude that you are talking about?
I will direct your attention back to the first post in the thread that explained reasonably well.
Gary Gygax, co-creator of Dungeons and Dragons, was found dead in his home in the morning of March 4th. He was 69.
Gary is in many ways the father of modern RPG's. He helped create the biggest, and best, paper and pen game on the planet. And most RPG's today bear his mark in some way, every computer based games. Without him, the land of fantasy would not be so bright, so magical, and it wouldn't be the dream we all wish would came true.
Now that is I call a legacy.
EDIT: I now cast 21 Magic Missile Salute!
As for what that means, you could find this pretty easily I think on the Web, but the short form is, back in the 70s, he co-created a style of game where you sit around a table each taking on the role of a character in a fantasy setting (like the Tolkien Lord of the Rings books) and play through a story run by a game master. It's not a fantastic example, but they were playing a Dungeons & Dragons in the movie 'E.T. The Extra-Terrestrial' early in the movie before E.T. is discovered.
There are aspects of improv theater, storytelling, but also tactics and random chance (represented by funny looking dice). It's modelling fantasy life, so the game doesn't have a winner or necessarily even an end. Characters develop over time, gaining powers and occasionally getting killed (possibly to be resurrected, or you just have to start a new character). You play for until people want to stop (better if you reach some natural stopping point in the story) and reconvene later to pick up where you left off. A good set of characters can be played for years.
This was something that was pretty big in the late 70s and early 80s when video games were in their infancy and there weren't so many distractions for geeks like myself. After the introduction of Dungeons & Dragons, games modelling other genres popped up all over dealing with spies, superheroes, horror, and even westerns and cartoons. These games lost favor with easier passtimes that push similar buttons, but there's really no substitute for the depth and interaction of real people right in front of you. They take time to play and time to prepare for, so I don't get to do it as much as I'd like, but I have friends I've been playing with since high school and I don't think we'll be stopping any time soon.
That's why we're sad to see Gygax go.