Byzas (seventh century B.C): Greek colonist who founded a namesake city on the Bosphorus: Byzantium.
Constantine the Great (r. 306-337): Roman emperor who legalized Christianity and moved the capital of his vast empire from Rome to Byzantium (which became known as Constantinople).
Justinian (r. 527-565): Byzantine emperor who expanded the empire to its greatest extent, codified law, and built Hagia Sophia.
Rumi, a.k.a. Mevlana (1207-1273): Great Selçuk philosopher and mystic who inspired the order of Whirling Dervishes.
Osman I (1258-1326): Founder of a small Anatolian principality that eventually grew into a 600-year-long empire, which bore a modified version of his name—"Ottoman."
Sultan Mehmet II, the Conqueror (r. 1451-1481): Successfully laid siege to Constantinople, putting the Ottoman Empire on the map as a world power.
Sultan Süleyman the Magnificent (r. 1520-1566): With his wife Roxelana, vastly expanded Ottoman territory and financed many fine buildings.
Mimar Sinan (1489-1588): Süleyman's magnificent architect, whose grand but tastefully restrained buildings and monuments still rank among Istanbul's best.
Kösem (1590-1651): "Favorite" of Sultan Ahmet I, who ran the empire through her sultan sons as the most significant figure in a 150-year-long "reign of the ladies."
Mustafa Kemal Atatürk (1881-1938): The "Grand Turk" who liberated his people from Western invasion at the end of World War I, founded the modern Turkish Republic, and enacted sweeping reforms that made Turkey more European than Asian.

A City of Many Names

Istanbul has had several names through its history, including Byzantium, Nova Roma, Constantinople, Konstantiniye, and finally, Istanbul.
Byzantium, which means "the city of Byzas," was named for its legendary Greek founder. When Constantine proclaimed Byzantium as the new capital of the Roman Empire, the official name was changed to Nova Roma, or New Rome. However, the people of the city called it Constantinople, or "the city of Constantine." That name survived during the period of the Ottoman Empire as Konstantiniye, the Arabic interpretation of Constantinople.
So, when did the city's name become Istanbul? Actually, Constantinople was always Istanbul. The word "Istanbul" comes from the Greek phrase "(t)stinpoH(n)," which means "to the city." So when people used this phrase, it meant that they were going into the city...that is, to Constantinople. The Turks kept using the adopted version of this phrase, and called the city Istanbul. (s3)