It was King Galifar I who united the five nations of Khorvaire under one crown and established the Kingdom of Galifar which would rule the breadth and width of Khorvaire for almost 900 years before the devastating Last War tore the nation apart.
Born in -45 YK to the warlord of Karrnath, Galifar grew up during the ten-year-long conflict know as the Border Wars. He assumed leadership of Karrnath just before his 21st birthday upon the death of his father. The cruelty and shortsightedness that he saw while growing up during a decade of war between all of the Five Nations helped him to envision a united kingdom where life could be improved and all of the nations could achieve a higher level of civilization.
Galifar spent 24 years trying to achieve his dream, not by the cruelty and bloodlust of Karrn the Conqueror, but by building a strong army and then using negotiations, diplomatic approaches, winning the hearts of the people of the Five Nations, and when necessary, military campaigns. Finally, after eight years of preparation, two years of negotiations, and fourteen years of combined diplomacy and warfare, the other four nations surrendered.
Galifar ruled the combined Five Nations for 40 years before stepping down at age 85 to let his son, Cyre, assume the throne. During his combined 64 years as warlord of Karrnath and then King of the Nation of Galifar, he laid down the foundations of organizations and traditions that would last for almost 900 years, and some for even longer.
In -7 YK, Galifar's alliance with the Dragonmarked Houses gave them special status in his new kingdom.
In the first year of his reign as king of the Five Nations, he assigned each of his five children to act as governor-princes/princesses over one of the constituent nations. He also established the precedent that his oldest surviving child would assume the throne upon his eventual abdication or death.
By the second decade of his reign, the lands he ruled were being called the Kingdom of Galifar.
In 15 YK he established the Arcane Congress.
For ten years, from 28 YK to 38 YK, he fought the Galifar/Lhazaar war.
In 32 YK, the nations of Thaliost, Wroat, Metrol, and Daskara each adopt the name of their Governor-prince/princess, becoming the modern nations of Aundair, Breland, Cyre, and Thrane. Karrnath, having been named for Karrn the Conqueror, already bore the name of Galifar's eldest son - Karrn.
Over the course of his long reign, he would loose several of his children, and upon his abdication, his youngest son Cyre was the one who inherited the throne. Galifar lived another thirteen years, finally dying at the age of 98.