Been around forever.
In essence, when people figured out that he was the leader of Echo Mirage, and thus was one of teh world's first Deckers who also has access to the best gear on the planet, it made sense that he might also be the legendary decker FastJack. This ignores the time constraints of course, or why the CEO of one of the Big Ten would bother, but hey. RUmors, gotta love 'em. 
Has this been confirmed? I always thought the the Knight-EM connection was rumor.
Depends on how confirmed Knight being David Gallivan is. It's one of those "99% certain, but never stated as absolutely true" things. Teh Shadows have come to terms with the idea, but the majority population has no idea. (It's a popular subject of conspiracy Matrix sites, of course.)
Interesting side note: Knight is one of those "Mysterious, unknown history" guys who makes vague noises about the Crash having wiped out his history and whatnot, but there are quite a few 'distant cousins' in the corporation as well who use Knight, or a variation of it, as their own name. Does he support them? Does he allow them? Do they have leverage in some way? Are they too small to worry about? It's never gone into, but while he has no official relatives, he has quite a few 'claim to be' relatives. Always thought that was a neat thing.
