In fact the yoyo or yo-yo is considered the second oldest toy in history, the oldest being the doll. In ancient Greece, the toy was made of wood, metal and terra cotta. The Greeks decorated the two halves of the yoyo with pictures of their gods. As a right of passage into adulthood Greek children often gave up their toys and placed them on the family alter to pay homage.
Pedro Flores, a Philippine immigrant, began manufacturing a toy labeled with that name. Flores became the first person to mass-produce toy yoyos, at his small toy factory located in California.
Duncan's first contribution to yoyo technology was the slip string, consisting of a sliding loop around the axle instead of a knot. With this revolutionary improvement, the yoyo could do a trick called "sleep" for the first time