The Wonder Boy series is a series of arcade games and conversions for home systems, developped by Westone Bit Entertainment and published by Sega. The numbering of the series has caused quite some confusion.
The series consists of:
Wonder Boy (1986) – arcade action – ported to several 8-bit and 16-bit systems.
Wonder Boy in Monster Land (1987) – arcade action RPG – This was referred to as The Story of WonderBoy II in the end credits of the arcade, and was ported to several 8- and 16-bit systems, called "Monster World" on most Japanese ports. There was also a near-perfect PC Engine port called "Bikkuriman World".
Wonder Boy III Monster Lair (1988) – arcade action shooting – arcade and later PS2 ("Sega Ages").
Wonder Boy III: Dragon's Trap (1989) – Master System only, never released in Japan. In Japan, it's nonetheless known as "Monster World II Dragon's Trap"
Wonder Boy V Monster World III (1991) – Megadrive/Genesis game (released 1993 for the Master System in Europe)
Monster World IV (1994) – Megadrive/Genesis game – only released in Japan.