Known leaders of the Galactic Empire:

Dynasty Emperor Description
Kamble Frankenn the First Usually named as the first Galactic Emperor, his coronation marked the transition from the Trantorian Empire controlling half of the galaxy to a new order, a virtual Galactic Empire which slowly began to entirely dominate the Milky Way, but which was far from accepted and had to deal with rebellions, dynastic wars and serious periods of breakdown. Technically, the time of this new order as an official and galacticly accepted Galactic Empire would not begin until two thousand years after his rule.
Aburanis Emperor responsible for the laws known as "Law Codes of Aburanis" which included forbidding the denigration of public officers of the Empire
Stannell II Boy-Emperor who ordered that Emperor's insignia be raised in Earth's Council Chamber at Washenn. He was insane and was removed by assassination after two years of reign.
Edard I Stannell II's successor. He took back the order after the assassination, which ended in revolt, but he couldn't stop the unrest which had spread through the Empire, the seeds of its Fall.
Stannell III Emperor during the Earth Rebellion of 827 GE, in which a radioactive and sparsely populated Earth tried to revolt against the Empire by using a bio-weapon. The rebellion failed, thanks partly to Joseph Schwartz, thrown through time, and a mentalic amplifier. The Empire initially helped Earth recover, then effort was mysteriously abandoned.
Kandar V Emperor who constructed a huge island on Alpha, designated "New Earth", after effort for Earth to recover was abandoned, and arranged for the last inhabitants of Earth to be transported there in 900 GE. The colony survived until at least 498 FE.
Leon the Libertine A brutal yet widely loved Emperor who ruled around 1,000 GE. Some considered his reign the most ancient of the Good Old Days, when order seemed natural and th Empire expanded into fresh worlds without trouble. He once arranged an entire faux-banquet for his ministers; the fruit could be bitten, but then snagged the guests' teeth, which remained firmly embedded until released by a digital command from the Emperor, after some amusing beggin and groveling before the other guets. Rumors persisted of darker delights obtained by Leon from similar traps, though in private quarters.
Ammentic the Great The earliest known Emperor of the period beginning circa 2000 GE in which the Galactic Empire was an official organisation accepted across the Galaxy. Around 2150 GE, he built the Imperial Palace, which was used until at least 195 FE.
Shoree-Han Empress in 3,000 GE. With support of Calvinian robots, she tried to introduce a new calendar and shake up social rigidity without success.
Kamble Emperor whom the long-lasting Kamble dynasty was named after, who ruled between the 3,000s and 6,000s GE. Wrote nine oracles containing his wisdom.
Eldonian's Clan Eldoninan the Elder The longest-lived Galactic Emperor, and the only one of his clan to die of old age. He once said, "Fame is the accumulation of misunderstanings around a well-known name."
Omar the Impaler Ruthless Emperor. During his reign, in Zone Sagittarius, he killed many.
Dacian A dynasty of Emperors who ruled in the early 7,000s GE. Some of their descendants became the Mayors of the Wye sector of Trantor.
Krozlik the Crafty Emperor during the late 7,000s GE. During his reign, a prosperous Zone finished sending the Mountain of Majesty to Trantor - it had taken seven centuries by slow boat. He directed it set on the horizon of his palace, where it towered once the city as the most imposing creation of that age.
Loris VI Emperor who developed the use of the Previous Inclosure strategy in the 10,000s GE.
Dadrian the Frugal Emperor who urinated in the Imperial Gardens
Wyan A dynasty of Emperors who ruled around the 11,500s to 11,800s GE. Their last Emperor, who preceded Agis VI, was a boy-emperor of too much ambition who had the Mountain of Majesty knocked down for an even more grandiose project which was also gone by the 12,000s.
Agis Agis VI Emperor who ruled for 42 years before the Entun dynasty, around 11,830 GE, and kept order in a prosperous Empire with a firm but non-tyrannical hand. He was also known for failing to control the news function of the Imperial Library.
Entun Manowell Known as Bloody Emperor Manowell. First Emperor of the great Entun dynasty
Elinor IV Emperor ruling around 11,900 GE. He had a mausoleum
Cleon's Grandfather Grandfather of Cleon, father of Stanel. He reinstated many Ruellian traditions.
Stanel VI Father of Cleon I.[1] His Chief of Staff was Eto Demerzel (R. Daneel Olivaw). Fortunate enough to escape the roughly one-in-two chances of assassination faced by the last century of Galactic Emperors.
Cleon I The last Emperor of the Entun dynasty, born 11,988 GE, died 12,038. He was Emperor when Hari Seldon first arrived on Trantor. He succeeded to the Imperial throne in 12,010 GE[1] at the age of twenty-two following the death of his father. Cleon was an amiable man, eager to treat others as hig equals yet not capable of conversing comfortably. Arguably, the most significant event of Cleon's rule occurred in 12,020 GE, when the young mathematician Hari Seldon came to Trantor and revealed that Psychohistory was a theoretical possibility. Cleon I’s reign represented a curious interval of quiet between troubled times, due to the skills of R. Daneel Olivaw, under the guise of his Chief of Staff, Eto Demerzel. Demerzel became aware that Seldon could possibly develop a mathematical method for predicting future history, and he (indirectly) informed the Emperor, who took an immediate interest in the matter. While Cleon was content to use Seldon as a source of self-fulfilling prophecies—a tool to prevent unrest—Demerzel had come to believe that the Empire itself was dying, and that only an honest investigation could prevent its fall or at least minimize that fall's effects. Therefore, Demerzel took steps to promote Seldon's development of his infant science. After Demerzel's retirement, Cleon appointed Seldon to be his new Chief of Staff, a position now termed First Minister. Seldon exerted himself to the fullest, employing pragmatic measures to halt anti-Imperial conspiracies while simultaneously developing psychohistory into a system capable of making solid predictions. Unfortunately, Cleon's personal ineptitude became his downfall. Wishing to thank a gardener, Mandell Gruber, for his part in thwarting an assassination attempt on Dr. Seldon, he promoted Gruber to Chief Gardener over the Imperial Palace grounds. Gruber, not wishing to abandon his lifestyle, overcame his timidity and shot the Emperor.
Interregnum between 12,038 and 12,058 GE. The chaotic upset which followed Cleon's assassination saw the rise of a Military Junta and Hari Seldon's retirement from overt politics.
Agis XIV Emperor who came to the throne after the fall of the Military Junta in 12,058 GE. Third cousin, on his mother's side, to Cleon I. Liked to be called the "Citizen Emperor" and befriended Hari Seldon although failed to use his meagre resources to assist the Psychohistory Project. A weak emperor with no actual power; controlled by the parliament. It has been said that he was crowned against his will and agreed because he was the only one that could inherit the crown from Cleon.
Daluben IV In Foundation and Empire, it is said Hari Seldon lived during his reign and he is implied to have been Emperor during the trial. This is contradicted by the prequels, in which it is shown that the major Emperors of Hari's life were Cleon I and Agis XIV, and that the Emperor during the trial was Klayus I. It is most likely that Daluben ruled during the early 12,060s GE, between the end of Agis XIV's reign and the beginning of Klayus I's short one.
Chen Klayus I Puppet emperor under the influence of his relative, Chief Commissioner Linge Chen of the Comission of Public Safety, during the time of the Seldon Trial on Trantor in 12,067 or -2 FE. He was deposed by Linge and the General Prothon shortly after the trial due to his alliance with Farad Sinter against Linge and the Comission to gain Imperial power again.
Divart Semrin Another Puppet Emperor of Linge Chen, who ruled in 12,068. The last Emperor of the Galactic Era - all Emperors after him ruled in the Foundation Era, which began in 12,069.
Stannell VII Ruler of the Normannic Sector. Last good ruler of the Provinces, under whom Siwenna almost achieved its ancient prosperity. Died in 104 FE.
Ricker the Usurper Ruled around 150 FE, Overthrown by Cleon II's father
Cleon II Commonly called 'The Great'. The last strong Emperor of the First Empire, ruling from 155 to 203 FE, he was important for the political and artistic renaissance that took place during his long reign. The great-grandson of a pirate ruler, he had three sons. During his later years he suffered from a painful and undiagnosed ailment. In 200 FE, he declared war against the First Foundation in Terminus, of which his Privy Secretary Ammel Brodrig informed him after learning about Riose's actions. Brodrig informed his Emperor that Riose was in the Lemul Cluster, that he was one of the "popular generals", and that his soldiers were entirely under his command. Cleon later recalled Riose and Brodig, ending the Fourth Seldon Crisis. He died in 203 FE but was remembered until at least 498 FE.
Dagobert Dagobert VIII One of the last Emperors of the Galactic Empire, fled Trantor to Delicass, renamed Neotrantor, which was about three parsecs away, during the Great Sack by the rebel Gilmer in 255 FE
Dagobert IX One of the last emperors of the Galactic Empire. He fled the Great Sack of Trantor along with his family. When visited upon by Ebling Mis, Toran and Bayta Darell, and the Mule in 295 FE, Dagobert IX was old and detached from reality, still reminiscing about imperial times long gone. Nevertheless, after he gave permission to Elbling Mis to use the Great Library of Trantor, he made a dignified impression as befits a Galactic emperor. His son, the crown prince Dagobert, tried to conspire under the influence of the corrupt governor Jord Commason. The crown prince was killed by the Mule with the help of a Visi-sonor.
Last Emperor The final unnamed Emperor of the Galactic Empire, who succeeded Dagobert around 300 FE and died on Neotrantor in 355 FE, the final end of the Empire