Tandem bikes are bicycles built for two. they handle really badly, but the upshot is some form of togetherness and the guy in the back doesnt need to know how to ride a bike.

what is the guy in the back called?

he is called a STOKER !

in a tandem bike, the guy in the front is called the "captain" and the guy in the back is known as the "stoker" some tandem bikes have two brakes in the rear tire, a rim brake and a drum brake. the rim brakes front and rear are usually controlled by the captain, while the rear drum brake is controlled by the stoker, applied at the direction of the captain. the extra brakes may be needed due to the added weight of two riders on long descents.