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.
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.
The starters also have the Pledge moves that are exculsive to them: Bulbasaur, Chikorita, Treecko, Turtwig and Snivy have Grass Pledge, Charmander, Cyndaquil, Torchic, Chimchar and Tepig have Fire Pledge and Squitle, Totodile, Mudkip, piplup and Oshawott have Water Pledge.
The rival trainer you come across will always pick your Pokemon's weakness, with a few exceptions.
Thus far, all Fire-type starters have a flame somewhere on their bodies by their final evolution. Three of them, Charmander, Cyndaquil, and Chimchar, have such a flame from the beginning.
In the first five Generations the vast majority of fully evolved Fire type starters end up duel type with Typhlosion being the sole exception, however three out of five Grass type starters and three out of five Water type starters never gain another typing