historically, the ruler or monarch of a Mongol tribe (ulus). At the time of Genghis Khan (early 13th century) a distinction was made between the title of khan and that of khākān, which was the title Genghis assumed as Great Khan, or supreme ruler of the Mongols. The term khan was subsequently adopted by many Muslim societies. Among the Seljuqs and the Khwārezm-Shāhs of Central and Southwest Asia, khan was the highest title of the nobility; in Ṣafavid Iran, it denoted a type of provincial governor. The meaning of the term eventually extended downward along the socioeconomic scale until khan became an affix to the name of any Muslim property owner, particularly in Afghanistan, Pakistan, India, and Bangladesh. It is now often used as a surname.