Cyrus Hamlin was a prominent American Congregational missionary and co-founder of Robert College in Constantinople.

Hamlin was born in Waterford, Maine, on January 8, 1811. He belonged to a prominent nineteenth-century family in the state. At sixteen, he entered an apprenticeship as a silversmith and jeweler in Portland, Maine, before deciding to enter the ministry. He first attended Bridgton Academy before heading to college. He graduated from Bowdoin College in 1834 and from Bangor Theological Seminary in 1837.

Hamlin married Henrietta Jackson in 1838 and they left the United States in the same year for the Ottoman Empire as a missionary under the American Board of Commissioners for Foreign Missions. He helped found Bebek Seminary in 1840 as part of his outreach to Armenians and directed it until 1860.