Bigfoot is unlocked when the player's Sim builds the Secret Warehouse. When the player first meets him, he tells them that he will bring joy to the guests if the player's Sim feeds him one item everyday. According to his stereotypical "Eh" at the end of each sentence, he is Canadian. He always seems to be in a happy mood while in the Secret Warehouse.
If you happen to find Bigfoot upset, it may be because he needs feeding.