Wonder Boy in Monster World, known in Japan as Wonder Boy V: Monster World III, is a side-scrolling action role-playing game originally developed by Westone and published by Sega for the Mega Drive/Genesis in 1991. It is the fifth game in the Wonder Boy series and the third game in the Monster World sub-series, following Wonder Boy in Monster Land (Super Wonder Boy: Monster World on the Japanese Sega Mark III) and Wonder Boy III: The Dragon’s Trap (Monster World II: Dragon no Wana on the Japanese Game Gear).

Versions for other platforms were also made. In 1993, Sega released a Master System version of the game specifically for the European market, while in 1994, Hudson Soft remade the game for the TurboDuo under the title of The Dynastic Hero (超英雄伝説ダイナスティックヒーロー, Chō Eiyū Densetsu Dainasutikku Hīrō), featuring an all-new theme and cast of characters. In 2007, the Turbo Duo and Mega Drive versions were re-released on the Wii Virtual Console download service.