Ragnarok Online had Steam trading card support added on July 29, 2014. There are 8 cards in the series. Because Ragnarok Online is a Free to Play Game, cards are earned by purchasing in-game content (approximately $9 USD per card drop).
The European Version of Ragnarok Online has a different set of trading cards. While European players can't play this version of the game, they can collect the cards (via trading or the Steam marketplace) and craft the badges.