Gondor founded by Isildur
Gondor is a fictional kingdom in J. R. R. Tolkien's writings, described as the greatest realm of Men in the west of Middle-earth at the end of the Third Age. The third volume of The Lord of the Rings, The Return of the King, is largely concerned with the events in Gondor during the War of the Ring and with the restoration of the realm afterward. The history of the kingdom is outlined in the appendices of the book.
Gondor was founded by the brothers Isildur and Anárion, exiles from the downfallen island kingdom of Númenor. Along with Arnor in the north, Gondor, the South-kingdom, served as a last stronghold of the Men of the West. After an early period of growth, Gondor gradually declined as the Third Age progressed, being continually weakened by internal strife and conflict with the allies of the Dark Lord Sauron.  By the time of the War of the Ring, the throne of Gondor is empty, though its principalities and fiefdoms still pay deference to the absent king by showing their loyalty to the Stewards of Gondor. The kingdom's ascendancy was restored only with Sauron's final defeat and the crowning of Aragorn as king.
Based upon early conceptions, the history and geography of Gondor were developed in stages as Tolkien extended his legendarium while writing The Lord of the Rings. Critics have noted the contrast between the cultured but lifeless Stewards of Gondor, and the simple but vigorous leaders of the Kingdom of Rohan, modelled on Tolkien's favoured Anglo-Saxons. Scholars have noted parallels between Gondor and the Normans, Ancient Rome, the Vikings, the Goths, the Langobards, and the Byzantine Empire.Númenórean kingdom
The shorelands of Gondor were widely colonized by the Númenóreans from the middle of the Second Age, especially by Elf-friends loyal to Elendil. His sons Isildur and Anárion landed in Gondor after the drowning of Númenor, and co-founded the Kingdom of Gondor. Isildur brought with him a seedling of Nimloth (Sindarin: nim, "white" and loth, "blossom") the Fair, the white tree from Númenor. This tree and its descendants came to be called the White Tree of Gondor, and appears on the kingdom's coat of arms.  Elendil, who founded the Kingdom of Arnor to the north, was held to be the High King of all the lands of the Dúnedain. Isildur established the city of Minas Ithil (Sindarin: "Tower of the Moon") while Anárion established the city of Minas Anor (Sindarin: "Tower of the Sun").Sauron survived the destruction of Númenor and secretly returned to his realm of Mordor, soon launching a war against the Númenórean kingdoms. He captured Minas Ithil, but Isildur escaped by ship to Arnor; meanwhile, Anárion was able to defend Osgiliath. Elendil and the Elven-king Gil-galad formed the Last Alliance of Elves and Men, and together with Isildur and Anárion, they besieged and defeated Mordor. Sauron was overthrown; but the One Ring that Isildur took from him was not destroyed, and thus Sauron continued to exist.Both Elendil and Anárion were killed in the war, so Isildur conferred rule of Gondor upon Anárion's son Meneldil, retaining suzerainty over Gondor as High King of the Dúnedain. Isildur and his three elder sons were ambushed and killed by Orcs in the Gladden Fields. Isildur's remaining son Valandil did not attempt to claim his father's place as Gondor's monarch; the kingdom was ruled solely by Meneldil and his descendants until their line died out.