Which Pokémon game pair introduced the Dark and Steel types?

Pokémon Gold and Silver introduced the Dark and Steel types.

The games formed the second generation of the main Pokémon series and added 100 new species to the original roster. Their new types expanded the battle system beyond the types available in the first-generation games.

Dark-type Pokémon and moves were designed partly to provide new strategic relationships with existing types. Steel-type Pokémon added a defensive specialty, with many resistances that made the type particularly influential in competitive battling.

Gold and Silver also introduced Baby Pokémon, breeding, held items, real-time day-and-night changes, and the Johto region. They were first released in Japan on 21 November 1999. The later Pokémon Crystal enhanced edition retained the generation's new types and systems.