Gary Gygax and Dave Arneson, for the creation of D&D, without which gaming would be very, very different. They invented hit points!
Also, Shigeru Miyamoto, for similar reasons: he changed the face of gaming.
And Shigesato Itoi, creator of the Mother/Earthbound series. No game has ever moved me as much.
On a non-gaming related topic, Hayao Miyazaki, for his films. He's like Disney, without the bad bits.
Terry Pratchett, for his intelligent, witty and hilarious novels.
I know, all in the world of entertainment. Don't care, they are all geniuses who hold a special place in my heart.