Of humble tribal origin, Karim Khan Zand became one of the generals of his predecessor, Nader Shah. In the chaotic aftermath of Nader Shah's assassination in 1747, Karim Khan became a major contender for power but was challenged by several adversaries. Karim Khan gained control of central and southern parts of Iran. In order to add legitimacy to his claim, Karim Khan in 1757 placed on the throne the infant Shah Isma'il III, the grandson of the last official Safavid king. Isma'il was a figurehead king, real power being vested in Karim Khan. He was a compassionate ruler who refused to assume the title of shahanshah (king of kings) but used that of the vakil (regent).
By 1760 Karim Khan had defeated all his rivals and controlled all of Iran except Khorasan, in the northeast, which was ruled by Shahrokh, the blind grandson of Nader Shah. During Karim Khan's rule Iran recovered from the devastation of 40 years of war. He made Shiraz his capital, constructing many fine buildings. Moreover, he reorganized the fiscal system of the kingdom, removing some of the heavy burdens of taxation from the agricultural classes. An active patron of the arts, he attracted many scholars and poets to his capital.
Karim Khan also opened Iran to foreign influence by allowing the English East India Company to establish a trading post in Bushire, the Persian Gulf port (1763). In advancing his policy of developing trade, in 1775-76 he attacked and captured Basra, the Ottoman port at the mouth of the Persian Gulf, which had diverted much of the trade with India away from Iranian ports.