In the E3 2009 Final Fantasy XIII trailer, there is a dude with silver hair. We didn't know his name and called him "The Dude With Silver Hair". But he has a name, and it's not that.
The fellow's name is Yaag Rosch. He is a lieutenant colonel and, yes, has silver hair. He's a silver fox! He's apparently the rival of heroine Lighting and desires peace for the citizens of FFXIII's Cocoon.
This info comes via Japanese mag V-Jump, which still lists the game's release date as simply "Winter 2009".
V-Jump: New Final Fantasy XIII Details - New Character Named [Final Fantasy-XIII.net]