The Exxon Building, more widely known by its address, 1251 Avenue of the Americas, was part of the later Rockefeller Center expansion (1960s-1970s) dubbed the "XYZ Buildings" on Sixth Avenue, (also known as Avenue of the Americas). Their plans were first drawn in 1963 by The Rockefeller family's architect, Wallace Harrison of the architectural firm, Harrison and Abramovitz.
Their letters correspond to their height. 1251 is the "X" Building as it is the tallest 750 ft (229 m) and 54 stories, but was the second one completed (1971). The "Y" is the McGraw-Hill Building, at 1221 Avenue of the Americas, which was the first completed (1969) and is the second in height (674 ft - 51 stories). The "Z" Building, the shortest and the youngest, is the Celanese Building at 1211 Avenue of the Americas with 45 stories (592 ft).
1251 is the second-tallest building in the whole of Rockefeller Center, after the GE Building.
Despite being one of the 100 tallest buildings in the United States, 1251 Avenue of the Americas is all but impossible to see from more than just a few blocks away as it is flanked on all sides by buildings over 500 feet tall. The result is that even though 1251 Avenue of the Americas is approximately as tall as the tallest buildings in cities like Boston or Minneapolis, it has almost no presence on the New York City skyline.
Although all three buildings are named after American companies, only McGraw-Hill remains in its eponymous skyscraper. The Celanese Building is now known as the News Corporation Building, when that media company anchored its high-profile headquarters there (complete with news ticker wrapped around the base). The Celanese tower is also the home of Fox News Channel.
ExxonMobil Corporation subsequently moved its headquarters to Irving in Texas, and its New York offices to Brooklyn; it no longer retains a presence in Rockefeller Center.
Inside, on the western end of 1251's atrium hangs an artist-authorized replica of a tapestry Pablo Picasso created for the ballet Mercure, the original of which hangs in the Musée National d'Art Moderne in Paris, France. It was created specifically for 1251, as per the plaque beneath it.