Mike Garson, born July 29, 1945, first became famous while working with David Bowie in the 1970s, on the Ziggy Stardust tour, and particularly for the avant garde jazz piano solo in the song Aladdin Sane. He has also worked with Nine Inch Nails, and has released a number of solo works.
Garson first joined the Pumpkins as a touring keyboardist on their Adore tour in 1998-99. He collaborated with Billy Corgan on the 1999 soundtrack for Stigmata, and joined the band again as a touring pianist/keyboardist on their 2000 Machina tour. He played at their VH1 Storytellers taping, and on shows from their European leg on through the band's final show. He also played a lengthy piano solo based on the Le Deux Machina theme, parts of which are included in the middle section of "Glass and the Ghost Children". The full solo can be found on the "Friends & Enemies of Modern Music" bootleg.
For more info, see Mike's twitter and official web site