PLAYERUNKNOWN'S Battlegrounds, or PUBG for short, is largely responsible for starting the current trend of Battle Royale games. It may have lessened in popularity following the launch of Fortnite and other similar games, but it still has a respectable following. In fact, it just passed 100 million downloads on the Play Store.
It's worth noting that the Play Store count doesn't include downloads originating from China, where the game is massively popular. Still, that's a respectable number of downloads, though Fortnite is quickly catching up.