Which Pokémon games were the first in the series to support online play through Nintendo Wi-Fi Connection?

Pokémon Diamond and Pearl were the first Pokémon games to support online play through Nintendo Wi-Fi Connection. Released for Nintendo DS in Japan in 2006, they let players trade and battle over the internet.

Earlier games supported local link-cable or infrared-style connections, but Diamond and Pearl connected trainers remotely through Nintendo's online service. The Global Trade Station also allowed players to search for and offer Pokémon worldwide.

The games introduced the Sinnoh region and 107 new Pokémon, including Dialga, Palkia and the starter trio Turtwig, Chimchar and Piplup. Their dual-screen interface used the lower screen for menus and touch controls.

Nintendo Wi-Fi Connection was discontinued in 2014, so the original online services no longer operate. Later Pokémon titles moved online features to newer Nintendo network systems and services.