Ismail I, also known as Shah Ismail, was the founder of the Safavid dynasty of Iran, ruling as its King of Kings (shahanshah) from 1501 to 1524. His reign is often considered the beginning of modern Iranian history, as well as one of the gunpowder empires.

The rule of Ismail I is one of the most vital in the history of Iran. Before his accession in 1501, Iran, since its conquest by the Arabs eight-and-a-half centuries earlier, had not existed as a unified country under native Iranian rule, but had been controlled by a series of Arab caliphs, Turkic sultans, and Mongol khans. Although many Iranian dynasties rose to power amidst this whole period, it was only under the Buyids that a vast part of Iran properly returned to Iranian rule (945–1055).

The dynasty founded by Ismail I would rule for over two centuries, being one of the greatest Iranian empires and at its height being amongst the most powerful empires of its time, ruling all of present-day Iran, Azerbaijan Republic, Armenia, most of Georgia, the North Caucasus, Iraq, Kuwait, and Afghanistan, as well as parts of modern-day Syria, Turkey, Pakistan, Uzbekistan, and Turkmenistan. It also reasserted the Iranian identity in large parts of Greater Iran. The legacy of the Safavid Empire was also the revival of Iran as an economic stronghold between East and West, the establishment of an efficient state and bureaucracy based upon "checks and balances", its architectural innovations, and patronage for fine arts.

One of his first actions was the proclamation of the Twelver denomination of Shia Islam as the official religion of his newly-founded Persian Empire, marking one of the most important turning points in the history of Islam, which had major consequences for the ensuing history of Iran. He caused sectarian tensions in the Middle East when he destroyed the tombs of the Abbasid caliphs, the Sunni Imam Abu Hanifa an-Nu'man, and the Sufi Muslim ascetic Abdul Qadir Gilani in 1508. Furthermore, this drastic act also gave him a political benefit of separating the growing Safavid Empire from its Sunni neighbors—the Ottoman Empire to the west and the Uzbek Confederation to the east. However, it brought into the Iranian body politic the implied inevitability of consequent conflict between the Shah, the design of a "secular" state, and the religious leaders, who saw all secular states as unlawful and whose absolute ambition was a theocratic state.