The Galactic Empire is the creation and subsequent leader, a senator from Naboo known as Palpatine after he has taken control of the Senate at the end of Star Wars III - Revenge of the Sith. At his command are millions of clone storm trooper or even billions of Stormtrooper given the sheer numbers of planets that are under his control. Only when the Emperor has been killed will the Empire disolve. As there is to be a new trilogy, they'll be someone in the wings hoping to recreate the Empire to control the galaxy. The Empire is controlled from Coruscant which was also the seat of power for the Old Republic.
Although the Death Star was not originally built by the Empire to start with, the Empire assumed control of it. The Death Star was built by the Separatists to protect themselves but that failed. When the first Death Star was destroyed, they subsequently ordered a second much bigger and more powerful Death Star to be built in orbit round the forest Moon of Endor. It was only when the second Death Star which the Emperor himself was visiting did the Empire fall apart.
When Obi-Wan Kenobi killed General Grevious in a duel on Utapu, Palpatine put in motion the end of the Jedi Council and ordered his Stormtroopers to kill the remaining Jedi's calling them traitors. After the Jedis were killed off, Palpatine went to the Senate to declare the first Galactic Empire had been created.
Admiral Kendal Ozzel is the fleet admiral for the Empire as they attack the ice planet of Hoth where the rebel alliance have been hiding since the Rebels blew up the Death Star. As Ozzel bought the fleet out of hyperspace too close to the planet, thereby alerting the Rebels, Darth Vader telekinetically killed him as punishment. The actor 'Michael Sheard' is also known as the stern bow-tie wearing Mr Bronson in the British television series 'Grange Hill'.
Admiral Firmus Piett is promoted to Fleet Admiral in star Wars V - The Empire Strikes Back when Darth Vader teleknetically kills Admiral Ozzel for bringing the fleet out of hyperspace too early and thereby alerting the Rebel Alliance that the Empire has found them.
General Veers is the commander in charge of the AT-AT Walker team in the Battle of Hoth in star Wars V - The Empire Strikes Back. His objective is to get the batallion of stormtroopers in the cargo hold to the Rebellion base on the planet.
Moff Jerjerrod is seen at the start of Star Wars VI - Return of the Jedi telling Darth Vader that he needs more men to complete the new Death Star. His faces turn white in fear when Darth Vader tells him that Emperor Palpatine is coming to inspect the word. Jerjerrod tells Darth that he will double the work. Other scenes of him in the film were cut.