Warcraft
In 2004, Blizzard Entertainment moved the series away from the real-time strategy genre and released "World of Warcraft", a massively multiplayer online role-playing game (MMORPG). Requiring a subscription fee to be paid to play, it also introduced regular additional content to the series in the form of patches. "World of Warcraft" gained popularity worldwide, becoming the world's largest subscription-based MMORPG in 2008. The game reached a peak 12 million subscribers worldwide in October 2010. "World of Warcraft" has had seven expansions as of 2018. During the production of "", Blizzard co-founder Frank Pearce stated that "If there's a team that's passionate about doing another "Warcraft" [real-time strategy], then that's definitely something we would consider. It's nothing that we're working on right now, we have development teams working on "", "", "Diablo III", and when those teams are all off the projects they're working on, they'll be intimately involved in the discussions about what's next".
Hearthstone
Of the game types they explored, Team 5 soon focused on the collectible card game approach, given that many on the team and in Blizzard had played such games since their introduction. The team found it natural to build the card game around the existing "Warcraft" lore; according to production director Jason Chayes, "Warcraft" was already a well-known property, and the depth of characters and locations created for other games in that series made it easy to create cards inspired by those. They also saw that new players to "Warcraft" may be drawn into the other games through playing "Hearthstone". The team was able to pull concepts and art from the pre-existing "World of Warcraft Trading Card Game", first published in 2006 by Upper Deck and later by Cryptozoic Entertainment; when "Hearthstone" was near completion, in 2013, Blizzard terminated its license with Cryptozoic as to favor their pending digital card game. The addition of heroes, an aspect from the previous trading card game, was found to help personalize the game for the player to allow players to discover useful combinations of cards for each hero.