Brian Douglas Wells
The actors have said that they weren't aware of it. The writers have said that they were only minimally aware of it and their story is entirely made up by them. The producers (including Ben Stiller) say they were unaware of it.
Frankly, I don't buy it from the entire group (though am sure any one individual, other than the writers, might have been).
One reason why I say the the writer's had to know (something a spoiler here):