A Pokémon Trainer (ポケモントレーナー, Pokémon Trainer) is a human in the fictional world of Pokémon whose hobby, pastime, or profession is the collecting, caretaking, and competitive battling of any of the eponymous Pokémon creatures. The humans being the commanders of their custom-trained Pokémon in battles is as important as the abilities of the Pokémon themselves in all forms of Pokémon media.
From the very outset of the Pokémon franchise, the world of Pokémon had been established as an Earth-like world populated by humans and, notably, an infinitely diverse biomass of magical creatures called Pokémon (short for Pocket Monsters). In this world, humans are referred to as Pokémon trainers if they collect, take care of, and train Pokémon for use in competitive matches with those of other trainers called Pokémon battles, officially sponsored and otherwise. Other Pokémon-related hobbies and professions exist in the world, such as Pokémon breeding, and a wholly different activity is undertaken by Pokémon coordinators who groom their Pokémon for use in Pokémon contests more closely resembling dog shows, but by far the path of the Pokémon trainer is the "primary" sporting activity in the franchise. This is the main activity/quest that the "main" Pokémon RPGs feature; as such, a player of a Pokémon RPG is considered a Pokémon trainer himself or herself.
All main Pokémon games cast the player as a young Pokémon trainer ready to set out on a Pokémon journey across that game's region of the Pokémon world, on a quest to capture many species of Pokémon and, from them, train a team of Pokémon proficient enough in the sport of Pokémon battling that they may carry the trainer to victory against that region's Pokémon League. The trainer's traditional tool for capturing Pokémon is the Poké Ball, which is sold at Poké Marts in the game's various cities and comes in many distinctive varieties, and a new trainer receives a piece of high-tech equipment called the Pokédex, which functions as an encyclopedia for the Pokémon in that region which the trainer must fill up, among other adventuring gear.
Throughout each journey, the trainer will battle hundreds of other trainers as well as encounter countless Pokémon in the wild, and the trainer will be involved in subplots involving thwarting the schemes of criminal organizations of trainers, such as the first and second generation's Team Rocket, the third generation's Team Magma and Team Aqua (which one was battled depended on the game), the fourth generation's Team Galactic, the fifth generation's Team Plasma, and the sixth generation's Team Flare. While the Pokémon Trainers have been depicted as boys in every installment, from the Crystal version of the second generation onwards, the player has had the option to choose the gender of the trainer; from then on, each new set of installment has introduced a new pair of standard Pokémon trainer designs, such as a pair each for Pokémon Ruby and Sapphire, the GBA remake of the original (featuring a new redesign of the playable trainer from the original Red and Blue versions, called "Red" in the second generation and their remakes), and Pokémon Diamond and Pearl. A small concession made by the franchise to the changing times is the gradual change from the "rivals to the death" image of the first series (Red, Blue, and Yellow), to the now very casual friendly talk between the protagonist and their neighbor of Diamond and Pearl. In the Generation 3 games (Ruby, Sapphire, and Emerald) and Generation VI games (X and Y), the rival took the gender opposite to the one chosen by the player.
In Super Smash Bros.
In Super Smash Bros. Melee
During the planning stages of Melee, Sakurai considered including a playable trainer, who summoned the second generation starters, but decided against the idea as there wasn't enough time and resources for such a labor-intensive character. In the final game, trainers otherwise have no appearance in Melee outside of trophies.
In Super Smash Bros. Brawl
The Pokémon Trainer makes an official appearance as a playable entity in Super Smash Bros. Brawl, modeled after the male trainer design seen in the Red and Blue versions, and their remakes in which the design was from the character Red. However, it would be inaccurate to call him a playable "fighter", as selecting him is like selecting a Zelda/Sheik-style character with three switchable forms, which are the three Pokémon the Pokémon Trainer has in his collection: Squirtle, Ivysaur, and Charizard. The trainer visually issues commands in the background of the stage to the Pokémon in the foreground, corresponding with the actions input by the player to the current Pokémon as the real fighter. One, however, might say the player controls the Trainer, who commands the Pokémon.
Pokémon Trainer is ranked 29th on the current tier list in E tier. His tournament results have been surprisingly high due to the efforts of TheReflexWonder, but when he is excluded, he has had barely any tournament success.
In Super Smash Bros. 4
As the game does not support mid-match character changes, Pokémon Trainer does not return as a playable character in Super Smash Bros. 4. While Charizard became a standalone playable character, Squirtle and Ivysaur did not make such a transition. Pokémon Trainer, however, makes a cameo as a collectible trophy, alongside both Ivysaur and Squirtle. The default appearances of the playable characters from Pokémon X and Y also appear as a trophy.