Which popular toy has colored squares that you twist to solve?

Rubik's Cube

What river in the Underworld did souls cross guided by Charon? Who led the Haitian Revolution and died imprisoned in France? What federal holiday was officially declared by President Ronald Reagan in 1983 honoring a slain civil rights leader? Which U.S. city hosted the first World's Fair held in America in 1876, celebrating the country's centennial? What item allows Mario to shoot fireballs?