Pocket Monster Red and Green were released in 1996 in Japan, and later released as Pokémon Red and Blue in 1998. They followed several years of development and became sleeper hits.[23][24] Believing it to be a one-time product, Nintendo initially shipped 200,000 copies, a relatively low amount. Most media ignored the games, but largely by word-of-mouth stemming from the hidden character Mew's introduction,[23] their popularity gradually spread throughout Japan, selling a million units by the end of 1996.[25] They eventually became the best-selling video games ever in Japan, with 7.8 million copies sold,[26] and 45 million sold worldwide.[27] After becoming a national sensation in Japan, the franchise was introduced to the United States in September 1998,[28] going on to start a worldwide craze dubbed "Pokémania".[29]