Passage: The headquarters of the United Nations occupies a site beside the East River, on between 17 and 18 acres (6.9 and 7.3 ha) of land purchased from the real estate developer William Zeckendorf Sr. At the time, the site was part of Turtle Bay, which was filled with slaughterhouses and tenement buildings. By the 1910s, there was also a pencil factory and a gas company building in Turtle Bay, on the site of the current UN headquarters. The development of Sutton Place and Beekman Place, north of the current UN site, came in the 1920s. A yacht club on the site was proposed in 1925, but it proved to be too expensive.In 1946, Zeckendorf purchased the land with the intention to create an "X City" on the site.  This complex was to contain an office building and a hotel, each 57 stories tall, and an entertainment complex between them. The X City would have also had smaller apartment and office towers. However, the $8.5 million ($72 million in 2018) for X City never materialized, and Nelson Rockefeller purchased an option for Zeckendorf's waterfront land in Turtle Bay. The purchase was funded by Nelson's father, John D. Rockefeller Jr.. The Rockefeller family owned the Tudor City Apartments across First Avenue from the Zeckendorf site. The city, in turn, spent $5 million ($43 million in 2018) on clearing the land.

Question: Who funded the purchase?
John D. Rockefeller Jr.