Starter Pokémon

A Starter Pokémon is the first Pokémon given to a Pokémon trainer in a certain region. Most games in the series have three choices for a starter. Every starter is part of a three-stage evolution line. They evolve once around level 16, and again around level 36.

List of starters
With the exception of Pokemon Yellow, every main series Pokémon game gives the player the choice between a grass type, a fire type, and a water type Pokémon, all of which are at level 5. Some gain a secondary typing as they evolve, but Bulbasaur and Rowlett both have one before they evolve at all.

As a result of these types, each starter has a type advantage over one other in its trio while it has a disadvantage over the other. The grass type has an advantage over the water type, the water type has an advantage over the fire type, and the fire type has an advantage over the grass type.

Kanto
In Pokémon Red, Pokémon Blue, Pokémon FireRed, and Pokémon LeafGreen, the player has a choice between Bulbasaur, Squirtle, and Charmander. Bulbasaur (which is a dual Grass-Poison type) evolves into Ivysaur at level 16 and Venusaur at level 32. Charmander, a pure fire type, evolves into Charmeleon at level 16, and Charizard at level 36, at which point it gains the flying type. Squirtle, a pure water type, evolves into Wartortle at level 16, and Blastoise at level 36. All three of these Pokémon gained Mega Evolutions for their final evolution in Pokémon X and Pokémon Y.

In Pokémon Yellow, the player cannot choose between Bulbasaur, Charmander, and Squirtle. The only choice the player has is Pikachu. Originally, Professor Oak was going to give the player an Eevee, but the player's rival took it first, leaving you with a Pikachu. Pikachu refuses to evolve into Raichu if given a Thunder Stone. Which kinda sucks. Because Pikachu sucks as a starter in this game.

Johto
In the games of the Johto region (Pokémon Gold, Pokémon Silver, Pokémon Crystal, Pokémon HeartGold, and Pokémon SoulSilver), the player is given the choice between Chikorita, Cyndaquil, and Totodile. Chikorita evolves into Bayleef, then into Meganium. Cyndaquil evolves into Quilava then into Typhlosion. Totodile evolves into Croconaw, then into Feraligatr.