John Davison Rockefeller Jr. (January 29, 1874 – May 11, 1960) was an American financier and philanthropist. Rockefeller was the fifth child and only son of Standard Oil co-founder John D. Rockefeller. He was involved in the development of the vast office complex in Midtown Manhattan known as Rockefeller Center, making him one of the largest real estate holders in the city at that time. Towards the end of his life, he was famous for his philanthropy, donating over $500 million to a wide variety of different causes, including educational establishments. Among his projects was the reconstruction of Colonial Williamsburg in Virginia. He was widely blamed for having orchestrated the Ludlow Massacre and other offenses during the Colorado Coalfield War. Rockefeller was the father of six children: Abby, John III, Nelson, Laurance, Winthrop, and David.

John Davison Rockefeller Jr. was born on January 29, 1874, in Cleveland, Ohio, the fifth and youngest child of Standard Oil co-founder John Davison Rockefeller Sr. and schoolteacher Laura Celestia "Cettie" Spelman. His four older sisters were Elizabeth (Bessie), Alice (who died an infant), Alta, and Edith. Living in his father's mansion at 4 West 54th Street, he attended Park Avenue Baptist Church at 64th Street (now Central Presbyterian Church) and the Browning School, a tutorial establishment set up for him and other children of associates of the family; it was located in a brownstone owned by the Rockefellers, on West 55th Street. His father John Sr. and uncle William Rockefeller Jr. co-founded Standard Oil together.

He initially intended to attend Yale University but was encouraged by William Rainey Harper, president of the University of Chicago, to instead attend Brown University, then a Baptist-oriented university. Nicknamed "Johnny Rock" by his roommates, Rockefeller joined both the Glee and the Mandolin clubs at Brown, taught a Bible class, and was elected junior class president. Scrupulously careful with money, he stood out as different from other rich men's sons. He joined the Alpha Delta Phi fraternity and was elected to Phi Beta Kappa. In 1897, after completing nearly a dozen social sciences courses, including one on Karl Marx's Das Kapital, Rockefeller graduated with a Bachelor of Arts from Brown University.

After graduating from Brown, Rockefeller joined his father's business in October 1897, setting up operations in the newly formed family office at 26 Broadway in Manhattan, where he became a director of Standard Oil. He later also became a director at J. P. Morgan's U.S. Steel company, which had been formed in 1901. Junior resigned from both companies in 1910 in an attempt to "purify" his ongoing philanthropy from commercial and financial interests after the Hearst media empire unearthed a bribery scandal involving John Dustin Archbold (the successor to Senior as head of Standard Oil) and two prominent members of Congress.

In September 1913, the United Mine Workers of America declared a strike against the Colorado Fuel and Iron (CF&I) company in what would become the Colorado Coalfield War. Junior owned a controlling interest in CF&I (40% of its stock) and sat on the board as an absentee director. In April 1914, after a long period of industrial unrest, the Ludlow Massacre occurred at a tent camp occupied by striking miners. At least 20 men, women, and children died in the attack. This was followed by nine days of violence between miners, strikebreakers, the Colorado National Guard. Although he did not order the attack that began this unrest, there are accounts to suggest Junior was mostly to blame for the violence, with the awful working conditions, death ratio, and no paid dead work which included securing unstable ceilings, workers were forced into working in unsafe conditions just to make ends meet. In January 1915, Junior was called to testify before the Commission on Industrial Relations. Many critics blamed Rockefeller for ordering the massacre. Margaret Sanger wrote an attack piece in her magazine The Woman Rebel, declaring, "But remember Ludlow! Remember the men and women and children who were sacrificed in order that John D. Rockefeller Jr., might continue his noble career of charity and philanthropy as a supporter of the Christian faith."

He was at the time being advised by the pioneer public relations expert, Ivy Lee, and William Lyon Mackenzie King. Lee warned that the Rockefellers were losing public support and developed a strategy that Junior followed to repair it. It was necessary for Junior to overcome his shyness, go personally to Colorado to meet with the miners and their families, inspect the conditions of the homes and the factories, attend social events, and especially to listen closely to the grievances. This was novel advice and attracted widespread media attention, which opened the way to resolve the conflict, and present a more humanized version of the Rockefellers. Mackenzie King said Rockefeller's testimony was the turning point in Junior's life, restoring the reputation of the family name; it also heralded a new era of industrial relations in the country.

During the Great Depression, he was involved in the financing, development, and construction of the Rockefeller Center, a vast office complex in midtown Manhattan, and as a result, became one of the largest real estate holders in New York City. He was influential in attracting leading blue-chip corporations as tenants in the complex, including GE and its then affiliates RCA, NBC and RKO, as well as Standard Oil of New Jersey (now ExxonMobil), Associated Press, Time Inc, and branches of Chase National Bank (now JP Morgan Chase).

The family office, of which he was in charge, shifted from 26 Broadway to the 56th floor of the landmark 30 Rockefeller Plaza upon its completion in 1933. The office formally became "Rockefeller Family and Associates" (and informally, "Room 5600").