Galaga is the sequel of the successful 1979 arcade game Galaxian. Namco of Japan developed Galaga and licensed it to Midway for U.S. release in 1981. As in Galaxian, players must shoot enemy aliens attacking in large formations. Although similar in objective, Galaga features a number of improvements in gameplay that make it more challenging and more exciting than Galaxian. The new multi-level game increases in difficulty and speed as the game progresses. A bonus level- called a "Challenging Stage"- appears every few levels and allows players to score up to 10,000 bonus points each time. Other improvements include increased alien intelligence and the ability to shoot multiple bullets at a time. The legacy of Galaxian continued on with Galaga; the game quickly became an arcade hit. Galaga's success inspired the production of even more sequels: Galpus, Galaga 88, Galaxian 3, and Attack of the Zolgear.