Tahmasp I was an influential Shah of Iran, who ruled the longest reign of any member of the Safavid dynasty. He was the son and successor of Ismail I.
He came to the throne aged ten in 1524 and came under the control of the Qizilbash who formed the backbone of the Safavid Empire. The Qizilbash leaders fought among themselves for the right to be regents over Tahmasp, and by doing so held most of the effective power in the empire. Upon adulthood, however, Tahmasp was able to reassert the power of the Shah and control the tribesmen with the start of the introduction of large amounts of Caucasian elements, effectively and purposefully creating a new layer in Iranian society, solely composed of ethnic Caucasians.