Story (or as I like to say. LORE)
I'll make this as short as possible...
Bro existed->Pizzeria got destroyed while he was teleported away (didn't realize pizzaplex WAS destroyed.)->Finds a weird ahh hole when he explores the Pizzaplex after returning->Void->Factory (Foundation?)->Map Bot and Mask Bot try and kill Pan-Stan->Fail->Pan-Stan summons Bill Cipher->Mask Bot eats Bill Cipher->Mask Bot disappears forever->Map Bot gets notified by Overseer->Helps Overseer get his fucking soul back->Is now MTF Alpha-1 of The Foundation :D
The Overseer
Dr. Fundus