In an AMA Mark Ruffalo was asked "Who's your favorite Pokémon?"
Here was his response, "Squirtle. For some reason that was the first Pokemon I got on my Gameboy, when I was playing it - they would give you 2 different ones, Charmander or Squirtle, and I started with Squirtle, so I have a warm place in my heart for Squirtle."