Rubik's Cube is a puzzle cube, and the world's biggest selling toy of all time with over 300,000,000 (300 million) sold. It was invented in 1974 by Hungarian sculptor and professor of architecture Ernő Rubik. In a classic Rubik's Cube, each of the six faces is covered by nine stickers, each of one of six solid colours: white, red, blue, orange, green, and yellow. In currently sold models, white is opposite yellow, blue is opposite green, orange is opposite red, and some might replace blue with black or purple.