Donald Duncan

Duncan saw the Flores toy, liked it, bought the rights from Flores in 1929, and then trademarked the name Yo-Yo. 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. The original shape, first introduced to the United States was the imperial or standard shape. Duncan introduced the butterfly shape, a design that reverses the halves of a traditional imperial yoyo. The butterfly allowed the player to catch the yoyo on the string easily, good for certain tricks.

Donald Duncan also worked out a deal with the newspaper tycoon William Randolph Hearst to get free advertising in Heart's newspapers. In exchange, Duncan held competitions and the entrants were required to bring a quantity of new subscriptions for the newspaper as their entry fee.

The first Duncan Yo-Yo was the O-Boy Yo-Yo Top, the toy with a big kick for all ages. Duncan's massive factory produced 3,600 of the toys every hour making the factory's hometown of Luck, Wisconsin the YoYo Capital of the World.