Who did you think originally put Harry's name in the Goblet of Fire?

I'm rereading the Goblet of Fire, and I have to wonder, who did everyone then think put his name in the GOF? I always thought it was Igor Karkaroff or Albus Dumbledore himself, because he would have some weird preparing him for Voldemort test like this going on. Mad-Eye Moody was my last suspect, ha. But who did you think it was? Mad-Eye? Barty Crouch? Ludo Bagman? Someone else? I'd like to know your thoughts.