The slogan for Pokémon was "gotta catch 'em all". But I have never heard that when I was watching Pokémon in the Japanese original with Chinese sub. The Japanese phrase was something along the lines of "Pokémon, caught!" (ポケモンゲットだぜー). Another phrase was also "my goal, Pokémon master!" (めざせポケモンマスター ).
Where did the English phrase come from?
Where does this phrase comes from?
According to Bulbapedia, this phrase is a rough translation from the Japanese games :
The Japanese equivalent is Get Pokémon! (Japanese: ポケモンゲットだぜー！ Pokémon get da ze~!, also spelt ポケモンＧＥＴだぜー！)
When did the phrase Gotta catch 'em all first appeared?
While the previous answers are correct, it is important to notice that this phrase first appeared on both anime and game.
You can see on the North America's and European's version of the Gameboy game Pokemon Red and Pokemon Blue the same phrase :
But which one of the anime or the game came first?
As @DavePhD mentionned in the comments, Gotta catch 'em all is a registered trademark. One of its first registration on June 23, 1998 mentions
entertainment services, namely, arranging and conducting competitions in the field of playing video games; stage presentations; video game presentations relating to video games; production, presentation, distribution, and syndication of animation, motion picture films, and television programs; and production and presentation of video tapes
which includes both the anime and the game. So we can say that Gotta catch 'em all appeared with the general airing of Pokemon in the United States.
Note that the first episode was broadcasted before the game was released in the United States : the TV Show was aired on September 8, 1998 while the game was first sold on September 28, 19981.
1 Wikipedia links : the first episode and the games
The phrase comes from the English theme song of the animated series. The chorus is as follows:
Pokemon, gotta catch 'em all
Its you and me
I know it's my destiny
Pokemon, oh, you're my best friend
In a world we must defend
Pokemon, gotta catch 'em all
A heart so true
Our courage will pull us through
You can listen to it on youtube.
It comes from the folk song Dance me a Jig, which is based upon events in 1863 in South Carolina during the American Civil War.
I didn't want no posses chasing after me,
So I took all the livestock and set 'em free,
Now master's so mad that he's liable to bust,
'Cause he gotta catch 'em all while I'm kicking up dust.
See also the 1950 publication "Sing Out!".
