Wilbur is made of actual flesh and human parts added with mechanical and metal parts to make him so human and life-like. In this world over-taken by robots, your father was a scientist that helped make them. You begged your father to make you a brother, and he reluctantly agreed and that brother was Wilbur. But you can't let Wilbur leave because the other Androids can't see him or they'll attack. Though Wilbur is reluctant to let you leave the house at all either because he won't be with you.