How many Pokémon are in the first generation?

The answer is: 151

The first generation of Pokémon officially contained 151 creatures, though getting that final count wasn't as straightforward as you might think. While most players knew about the 150 Pokémon they could catch through normal gameplay, number 151 was a bit of a rebellious addition to the family.

During the final stages of development, programmer Shigeki Morimoto secretly squeezed one more Pokémon into roughly 300 bytes of freed-up space in "Pocket Monster Red and Green" (better known as "Pokémon Red and Blue" in the States). This sneaky addition was Mew, programmed in without Nintendo's knowledge after debugging features were removed. The company only discovered Mew's existence after the games were already on store shelves.

This secret addition sparked one of gaming's greatest urban legends. Players desperately searched for ways to find Mew, trying everything from pushing trucks near the S.S. Anne to surfing up and down specific coastlines hundreds of times. The hunt for secrets even led players to discover the infamous Missingno glitch, a broken character that appeared when players messed with the game's code. While Missingno wasn't an official Pokémon, it became legendary in its own right for its ability to duplicate rare items and generally mess with players' games in crazy ways.

Nintendo eventually embraced Mew's existence, distributing it through official events. But those original playground rumors about finding Mew under trucks? They're still circulating today.