Ash starts out with Pikachu. His next Pokemon he catches, Caterpie. It later evolves into Metapod then Butterfree, which he sets free to mate. He catches a Pidgeotto, and later in the Pokemon League, it evolves into Pidgeot and lets it stay there to protect a Pidgey and Pidgeotto.A Bulbasaur follows Ash on his quest, then Charmander, wich evolves into Charmeleon, then Charizard. A Squirtle from the Squirle Squad later decides to follow Ash. Then he captures a Krabby which evolves into a Kingler before the Pokemon Leagues. He then captures a Primeape, which he lets train with a fighting Pokemon trainer. He then captures a Muk. A Haunter also follows him during a period of time, but I wouldn't say he captured it. He also catches a Lapras and a tauros after the Pokémon league.Then when Brock leaves, he catches a Snorlax!