When Nader Shah was assassinated in 1747, there were at least four rivals for his throne. Among these the least likely to succeed was Karim Khan. Not only was his tribe small, but he himself had been a common soldier in Nader Shah's army, rising to a position of leadership by his ability.
Karim Khan joined with another Persian rival, Alimardan Khan of the Bakhtyari tribe, and they claimed to be "regents" in behalf of a minor Safavid prince. Later, when Alimardan was killed, Karim Khan was the sole ruler in southern Iran.
The third claimant was Azad, an Afghan general of Nader Shah who ruled in Azerbayjan. Azad went against Karim Khan and pushed him back all the way to Shiraz and beyond. Karim Khan, however, ambushed Azad and routed him in 1752. Azad took refuge in Baghdad and later in Tiflis but finally did not have any recourse but to put himself at the mercy of Karim Khan. He, behaving unlike the rulers of his time, treated Azad very kindly, and the two became close friends.
The last rival was Mohammad Hasan Khan Qajar, who ruled in northern Iran. Even though Karim Khan was no match for him in the field and was defeated in several battles, his popularity caused the allies of Qajar to desert to Karim Khan. In 1757 Mohammad Hasan was killed, and Karim Khan became the sole ruler of Iran.
For over 20 years Karim Khan gave the war-weary people of the country tranquility, security, and justice. The only exception was the short campaign against the Ottoman Empire, in which he captured Basra in order to save the trade of the Persian Gulf. From there he went and captured Baghdad in order to make it easy for the Persian Shiites to go on pilgrimage to Karbala.
Karim Khan never assumed the title of shah and was content with "vakil, " or regent. He chose Shiraz for his capital and beautified that already beautiful city with mosques, bazaars, baths, and gardens which bear his name to this day. At his death in 1779 the country was thrown again into chaos, and the struggle among his own relatives was the bloodiest.
Karim Khan is often praised for his generosity, modesty and fairness.
Quotes from others about the person
In the words of John Malcolm, "The happy reign of this excellent prince, as contrasted with those who preceded and followed him, affords the historian of Persia that kind of mixed pleasure and repose, which a traveler enjoys on arriving in a beautiful and fertile valley during an arduous journey over barren and rugged wastes. It is pleasing to recount the actions of a chief who, though born of an inferior rank, obtained power without crime, and who exercised it with a moderation that, for the times in which he lived, was as singular as his humanity and justice. "