are they an architectural group?
Yes - an American architectural firm by founding partners Charles Follen McKim, William Rutherford Mead and Stanford White
McKim, Mead &amp; White
McKim, Mead & White was an American architectural firm that came to define architectural practice, urbanism, and the ideals of the American Renaissance in fin de siècle New York. The firm's founding partners Charles Follen McKim (1847–1909), William Rutherford Mead (1846–1928) and Stanford White (1853–1906) were giants in the architecture of their time, and remain important as innovators and leaders in the development of modern architecture worldwide. They formed a school of classically trained, technologically skilled designers who practiced well into the mid-twentieth century. Arguably, only Frank Lloyd Wright was more important to the identity and character of modern American architecture. 
who owns the plaza hotel in new york Katara Hospitality what is the significance of this place? The Plaza hotel has been the meeting place for important political meetings; notable singers have performed in the Persian room; it has The Grand Ballroom, Terrace Room etc who are the aforementioned hospitality group? Katara Hospitality, formerly known as Qatar National Hotels Company, is the largest hotel owner, developer and operator in Qatar. It is government-owned. what is its history? Formed in 1970 as Qatar National Hotels Limited (QNH). In 1973, Marriott Hotel  owned by QNH, became the country's five-star hotel. In 1993, this company was replaced by Qatar Nationals Hotel Company. Eventually, in 2012, QNH was rebranded under its current form, Katara Hospitality. who designed the hotel mentioned in the beginning? McKim, Mead & White
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McKim, Mead &amp; White [SEP] Introduction
McKim, Mead & White was an American architectural firm that came to define architectural practice, urbanism, and the ideals of the American Renaissance in fin de siècle New York. The firm's founding partners Charles Follen McKim (1847–1909), William Rutherford Mead (1846–1928) and Stanford White (1853–1906) were giants in the architecture of their time, and remain important as innovators and leaders in the development of modern architecture worldwide. They formed a school of classically trained, technologically skilled designers who practiced well into the mid-twentieth century. Arguably, only Frank Lloyd Wright was more important to the identity and character of modern American architecture.