A game by Namco for the arcade, originally released in 1981.
In 1978, Space Invaders took the world by storm, popularizing shmup mechanics with its simple yet effective design. The game features rows of alien invaders marching back and forth along the top of the screen and slowly descending on the player's position. Enemies drop bombs and the player fires shots of his own, with only a row of barriers along the bottom of the screen to protect him, but these are worn down with each hit they take, even with friendly fire. As the player destroys his foes, they begin speeding their descent (a result of the original arcade processor being able to more quickly animate smaller numbers of sprites), becoming more menacing as the level wears on.
The popularity of this game led to other developers trying their hand at similar gameplay styles, but few were as popular as Namco's Galaxian, which was released in 1979, predating their most seminal arcade title, Pac-Man, by a matter of months.

Galaxian features multi-colored insect-based enemies (with true color, rather than overlays) that move back and forth along the top of the screen, but rather than simply dropping lower and lower, these enemies break off from their formation to dive bomb the player's ship.

In Galaxian, the player is able to attack dive-bombing enemies or focus his fire on the larger formation, but he can only have one bullet onscreen at a time. As a result, firing on the dive-bombing enemies presents a greater risk but also allows the player to fire more quickly if he hits his target. Once enough enemies are destroyed, they no longer return to the formation but rather continuously dive-bomb the player, and later levels allow more enemies to dive bomb simultaneously and fire more shots while doing so.

In Galaga, Namco refined this formula, making improvements in every aspect of gameplay. For starters, enemy waves fly across the screen in a line before taking their places in the formation, giving the player the opportunity to clear some of the enemies before they form up, but also giving the enemies a chance to drop bombs and send some of their ships down to dive bomb the player. Instead of simply marching back and forth, alien formations eventually pause and begin expanding and contracting. Once enough enemies have been destroyed, they begin to dive bomb they player continuously, with more ships doing this at once in later levels.

The game features three main enemy types, each with its own set of behaviors. The red enemy is fast and can drop straight down the screen. The yellow one can fly in circles, sometimes dropping below the player ship’s position at the bottom of the screen, and then circling back up to hit it from below. And finally, the most impressive baddie of all of them all… an enemy that takes two hits to destroy and can capture the player's ship.

This large ship dive bombs the player along with other enemies, but it sometimes halts and extends a tractor beam downward that can capture the player's ship when it comes in contact. The player has a bit of time to fire at the enemy ship before the tractor beam reaches him, or he can dodge out of the way, but if his ship is captured, the enemy moves back into formation with the player's ship in tow.

If the player manages to kill this enemy when it dive bombs again, he then recaptures his ship, allowing him to control two ships simultaneously for double the firepower. However, this endeavor has its risks, as the player may potentially destroy his own ship when trying to recapture it, and playing with two ships at a time makes the player a larger target for enemies, potentially causing him to lose additional lives. This mechanic adds a layer of strategy that had not previously been seen in games of this type.

A challenge stage appears every few levels where enemy waves enter the screen, fly though a pattern without dropping any bombs, and leave without entering a formation. Bonus points are awarded based on the number of ships destroyed during these stages, and destroying all 40 ships awards an additional bonus. Destroying every enemy relies somewhat on the player's knowledge of where enemies will emerge and what patterns they will perform. Having two ships makes it easier to achieve a perfect score in these stages, and the player is granted extra lives at certain score thresholds.

The player’s ship is faster and more maneuverable than its Galaxian counterpart, and 2 bullets can be onscreen at a time, allowing for a faster firing rate. As a result, a skilled player can stave off death as enemies become incredibly aggressive in later levels, increasing their speed, firing more shots, and descending in larger numbers. The game also offers some surprises in the form of enemies that can transform and spawn additional foes that speed ahead or trail behind them.

Namco continued to iterate on this formula with titles like Bosconian and Gaplus (later re-released as Galaga 3) before returning to the ever-popular Galaga foundation with the release of Galaga '88 and Galaga Arrangement, along with ports and emulations of Galaga for a variety of platforms, and the occasional new Galaga-themed effort such as the 3D rail shooter Galaga: Destination Earth and the fast-paced pattern-based Galaga Legions.

Galaga was developed by Namco, the developer behind a number of formative arcade titles from the late 1970's and early 1980's, including Pac-Man, Rally-X, Dig Dug, Pole Position, Xevious, and Mappy, as well as their subsequent sequels and spin-offs. The studio has gone on to re-release these games - along with various updates and new takes on their franchises - across numerous systems, while also developing entirely new popular series, including Ridge Racer, Ace Combat, Tekken, Klonoa, and Katamari Damacy. Bandai purchased Namco in 2005 and formed Bandai Namco Entertainment, which primarily focuses on releasing games that fall within Namco's established franchises.