Pokémon Gold and Silver introduced the Dark and Steel types.
These two types appeared with Pokémon’s second generation, which began with the Japanese release of Gold and Silver in 1999. They expanded the battle system beyond the original set of 15 types and helped rebalance matchups between Pokémon and moves.
The Dark type was designed partly to address the strength of Psychic-type Pokémon in the first generation. Steel, meanwhile, added a highly defensive type with many resistances. Their introduction also brought new Pokémon, moves, held items, breeding, a day-and-night system, and the Johto region.
Fairy is a later addition: it debuted in Pokémon X and Y in 2013. Dragon existed from the first generation, although the original games contained only one Dragon-type move and no fully Dragon-type Pokémon family. Because type additions are tied to generations, Dark and Steel are the canonical pair associated with Gold and Silver.