Depending on how you define custom cards, there might've been other people or companies before Ellusionist, but the Black Tiger deck was the deck that got the ball rolling big time. The name is a callback to an old USPCC deck called Tiger deck I believe.
I wasn't around back then, but I'm sure Jake can fill in with some more info if he stops by. He wasn't around then either, but he's a bot so he's bound to have more info on his harddrive.
TL;DR: Yes, we're somewhat guilty.