Hitmonchan first appeared in the first Pokémon games, Red & Blue. Challenging a fighting dojo in Saffron, the player's character is offered a choice of one of two Pokemon upon vanquishing the dojo's leader; the boxing-themed Hitmonchan, or its kicking counterpart Hitmonlee. While this was the only opportunity in the game to acquire these two creatures, neither of them were particularly useful. Hitmonchan had high attack, and modest defense and speed stats, but suffered from low HP, an inability to learn any noteworthy fighting attacks, and a terrible Special stat which made it vulnerable to special attacks, and also rendered its signature Elemental Punches useless in its hands.
Come Gold & Silver, Hitmonchan saw several improvements. It gained high Special defense when the Special stat was divded into 2 categories, the advent of breeding gave it access to Hitmonlee's superior Fighting moves, as well as making it easier to gain multiple Hitmonchans. Additionally, the 2 new Pokemon Types, Steel & Dark were both weak to fighting types, raising the usefulness of fighting types in general.
Laterer Pokémon games have further enhanced Hitmonchan, giving him access to more Fighting moves, usefull support abilities, and he even became proficient with his Elemental Punches when they were reclassified as physical moves.
The in-game encyclopedia, the Pokedex, describes Himtonachan's ability to punch threw concrete and throw punches faster than the eye can follow.