A Death Star was a moon-sized Imperial military battlestation armed with a planet-destroying superlaser.
The Death Stars, whose concept had been explored even before the Clone Wars, were the first in a long series of superweapons developed by the Galactic Empire. The Death Star was designed to allow Darth Sidious to more directly control the Empire through fear.
One Death Star was completely built by the Empire, with a second and third one never reaching full completion, as well as a prototype being in existence. In addition, a scaled-down version, the Tarkin, and a Huttknockoff, the Darksaber, would be created by the Empire and Durga the Hutt, respectively.
Both Death Stars were destroyed by the Rebel Alliance shortly after they became operational. The first Death Star was destroyed by Luke Skywalker, with the help of Han Solo, and the second Death Star was destroyed by Wedge Antilles and Lando Calrissian. Prior to the second Death Star being built, the Galactic Empire tested out a planetary superlaser for protecting its installations on the planet of Dubrillion. At some point after the second's destruction, the Rebel Alliance also attacked and destroyed a third Death Star. Following their destruction, other planet-devastating superweapons followed, including the Galaxy Gun, the Darksaber, the Sun Crusher, and the World Devastators.