The Dark type was introduced in Pokémon Generation II to help balance the powerful Psychic type. It first appeared in Pokémon Gold, Silver, and Crystal.
In the Generation I games, Psychic Pokémon had a major competitive advantage because few types could reliably counter them. Generation II added Dark Pokémon and Dark-type moves as part of a broader battle-system revision. Dark moves were super effective against Psychic Pokémon, giving teams a new strategic option.
Generation II also introduced the Steel type, which provided additional defensive answers to Psychic attacks. Dark and Steel were therefore both new types, but they served different roles: Dark focused on offensive matchups and immunity to Psychic attacks, while Steel brought high defensive resistances.
The Fairy type arrived much later, in Generation VI, and is sometimes mistakenly associated with the original anti-Psychic changes. Dark has remained an important type across the franchise, appearing in Pokémon such as Umbreon, Houndoom, Tyranitar, and the legendary Pokémon Darkrai.