After "Mario Bros.", Yokoi produced several R&D1 games, such as "Kid Icarus" and "Metroid". He designed R.O.B. and the Game Boy, the latter of which became a worldwide success. Another of his creations, the Virtual Boy, was a commercial failure. Nintendo has denied that the Virtual Boy's poor performance in the market was the reason for Yokoi's subsequent departure from the company, holding that his retirement was "absolutely coincidental" to the market performance of any Nintendo hardware. According to his Nintendo and Koto colleague Yoshihiro Taki, Yokoi had originally decided to retire at age 50 to do as he pleased but had simply delayed it. According to David Sheff's book "Game Over", Yokoi never actually intended for the console to be released in its present form. However, Nintendo pushed the Virtual Boy to market so that it could focus development resources on the Nintendo 64.