Starter Pokémon, or Starters, are the Pokémon a trainer chooses at the beginning of their Pokémon journey.
In each generation of Pokémon games, a set of Starter Pokémon are available for new trainers to choose from in sets of three; the types that make up these sets are Fire, Grass, and Water. However, Pokémon Yellow is currently the sole exception to all the above, with Pikachu as the only starter available to the player.
Bulbasaur is the only Starter to be dual-type in basic form.
All known Grass-type starters are based on pre-historic creatures and evolution. Venusaur has legs that lift it off the ground (a characteristic of dinosaurs), Meganium is based off a Apatosaurus, Sceptile is based of a Dilophosaurus, the Snivy-Serperior evolution represents the loss of hind legs (the transition from dinosaurs to snakes), and Chespin is based off the first mammal, the Megazostrodon. Also, each have a type of plant on their bodies which grows bigger through evolution.
Most Fire-type Starters' final evolutions consist of two types. The only exception is Typhlosion.
In Johto, the Starters stay pure Fire, Grass and Water types throughout their evolutions. They never gain a new typing.
All Water-type Starters are based on aquatic creatures (turtle, crocodile, axolotl, penguin, otter, frog).
Starter Pokémon have unique special abilities: all Grass Starters possess the ability Overgrow, all Fire Starters possess the ability Blaze, and all Water Starters possess the ability Torrent.
Except for Pikachu and Eevee, all the Starters in any form can learn the ultimate attacks. Bulbasaur, Chikorita, Treecko, Turtwig and Snivy can learn the ultimate Grass attack Frenzy Plant. Charmander, Cyndaquil, Torchic, Chimchar and Tepig can learn the ultimate Fire attack Blast Burn. And Squirtle, Totodile, Mudkip, Piplup and Oshawott can learn the ultimate Water attack Hydro Cannon.
However, both Eevee and Pikachu can learn what can be called the ultimate attacks in there respective type in any form. Pikachu can learn Volt Tackle, and Eevee in one of its evolved forms, can learn Hyper Beam.