There are many popular online slot game brands in the world, and the most popular ones can vary depending on the region and the preferences of the players. Some of the most popular online slot game brands include：

• NetEnt: This is a Swedish company that has been creating online slot games since 1996. Some of their most popular games include Gonzo’s Quest, Starburst, and Mega Fortune.
• Microgaming: This is a company based in the Isle of Man that is known for creating innovative and high-quality online slot games. Some of their most popular games include Mega Moolah, Immortal Romance, and Thunderstruck II.
• Playtech: This is a UK-based company that has been creating online slot games since 1999. Some of their most popular games include Age of the Gods, Beach Life, and Great Blue.
• IGT: This is an American company that has been creating land-based and online slot games for many years. Some of their most popular games include Cleopatra, Wolf Run, and Da Vinci Diamonds.
• Aristocrat: This is an Australian company that is known for creating innovative and engaging online slot games. Some of their most popular games include 50 Lions, Buffalo, and Miss Kitty.

It’s important to note that this is just a small selection of the many online slot game brands that are available. There are many other companies that create high-quality online slot games, and the popularity of these games can vary depending on the region and the preferences of the players.