In 1968, Hot Wheels were introduced in the United States by Mattel to address the complaint that they had no line of toys for boys to balance their line of Barbie dolls for girls. Because they looked fast and were fast (they were equipped with a low-friction wheels/axles), Hot Wheels quickly became the most popular die-cast cars in the toy market, becoming one of the world's top sellers, challenging the popularity of Matchbox.