Brain is Penny's dog who is the only one that knows Penny is the one who solves Gadget's missions. Brain typically has to follow Gadget to wherever he is going on his missions and has to disguise himself as a civilian to prevent Gadget from noticing him. Only to find out that Gadget thinks he's a M.A.D agent or another type of person, even though it's obviously him. Brain also fears Gadget and his gadgets to an extent so it's best not to bring him up in conversation.