The first ever confirmed Pokemon, was Rhydon. Trying to find dates now just want to post this, hope you don't mind :P
The first game was released in the United States on September 30, 1998. The first games, Blue, Red, and Yellow, would have the player being introduced to Pikachu, Bulbasaur, Squirtle, or Bulbasaur first. Official packaging had Venusaur and Pikachu on it.
This has absolutely nothing to do with your question but here is some very cool history on the Pokemon world. Link