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Timeline. 1  1965: Plans for the John Hancock Center are announced. 2  1969: Construction is completed. 3  1972: The Hancock Center is surpassed by the Standard Oil Building (now the Aon Center) as the tallest building in Chicago.  1973: The residential portion of this building converts from apartments to condominiums.
The company that built the Hancock Tower and two earlier, similarly named buildings is known loosely as John Hancock Insurance, or simply John Hancock. It was known as The John Hancock Life Insurance Company in the 1930s and The John Hancock Mutual Life Insurance Company in the 1940s.