Final answer:
Osman I founded the Ottoman Empire, which was expanded by Mehmed II after he conquered Constantinople in 1453. The empire spanned three continents and was later led by Suleiman the Magnificent, who extended its reach even further.
Step-by-step explanation:
The founder of an empire that eventually spanned three continents - Africa, Asia, and Europe - was Osman I, the leader of the Ottoman Turks. From its modest beginnings in the late 13th century, the Ottoman Empire grew to encompass significant territories across these continents.
The most significant expansion occurred when Mehmed II, also known as Mehmed the Conqueror, took Constantinople in 1453, which led to the vast growth and prosperity of the empire, making Istanbul one of the world's largest cities and controlling trade routes between Europe and Asia.
Under subsequent sultans such as Suleiman the Magnificent, the empire continued to expand its influence and control; in Suleiman's time, it posed a serious threat to Vienna and wielded significant power over the Mediterranean Sea and key trade hubs.
The Ottoman Empire was recognized for its military prowess, often labeled amongst the 'Gunpowder Empires,' and its tolerance towards religious and ethnic diversity contributed to its long tenure in history, lasting until the early 20th century.