John Jacob Astor III (June 10, 1822-February 22, 1890) was the elder son of William Backhouse Astor, Sr. and the wealthiest member of the Astor family in his generation, which meant one of the wealthiest men in the United States.

John Jacob III studied at Columbia College and Göttingen following which he went to Harvard Law School. He volunteered in the Union Army in the American Civil War and proved an efficient and capable soldier, rising to the rank of colonel and was brevetted Brigadier General for his service during the Peninsular campaign to capture Richmond, Virginia.

As a businessman, he dabbled in railroad investment, but was forced to yield control of the original New York Central Railroad line (from Albany to Buffalo) to Cornelius Vanderbilt. His principal business interest was of course the vast Astor Estate real estate holdings in New York City, which he managed profitably and parsimoniously.Unfortunately, some of his properties were an exploitation of the poor in an era when municipal authorities rarely enforced building codes.

In 1846 he married Charlotte Augusta Gibbes (c.1825-1887) of South Carolina and in 1859 he built a home at 350 Fifth Avenue, which is today the street address of the Empire State Building. Later, he added an imposing vacation home, Beaulieu, in Newport, Rhode Island.

John Jacob Astor III had little inclination to do much in the way of charitable works beyond continuing gifts made by his ancestors to the Metropolitan Museum of Art, Trinity Church, and the Astor Library. However, his deeply religious wife had quite a different attitude. Charlotte Astor supported the newly formed Children's Aid Society and sat on the board of the Women's Hospital of New York, an institution that to her dismay refused to accept cancer patients. Deciding to do something about it, she persuaded her husband to donate the money to erect the New York Cancer Hospital's first wing, appropriately named the "Astor Pavilion." By a twist of fate, Charlotte Astor died of uterine cancer.

Aristocratic by inclination, he increasingly visited London in his later years, and his only child, son William Waldorf Astor (1848-1919), would move there permanently with his family in 1891.

John Jacob Astor III is interred in the Trinity Church Cemetery in Manhattan, New York.