Pierpont Morgan’s name resonates as few others do. He was Wall Street’s most powerful man. His mergers and acquisitions included the creation of the first billion-dollar corporation, U.S. Steel. He was America’s greatest art collector in our golden age of collecting. And he was one of Manhattan’s great patrons of architecture. Morgan either built or was involved in the building of such buildings as Madison Square Garden at 26th Street, the Metropolitan Club, Grand Central Terminal, the north and south wings of the Metropolitan Museum of Art (of which he was president), the New York Yacht Club, and the University Club.

The building that bears Morgan’s name is the Pierpont Morgan Library. Actually, this is a group of buildings, on 36th Street between Madison and Park Avenues and on Madison between 36th and 37th Streets. Morgan built only one. And it’s worth taking a look at now.

Morgan was an established financier when, in 1880, he and his family moved into a large brownstone house on the northeast corner of Madison and 36th. It’s no longer there, but was similar to the old Phelps house (later the home of Morgan’s son) at the southeast corner of Madison and 37th, built in the 1850s. Morgan lived in this house until he died, in 1913.

In 1902-07, Morgan built an addition. This housed his study and his library. It was no ordinary library, but rather the finest privately owned collection of rare books and manuscripts in the world. It required no ordinary building.

Morgan asked Charles McKim, who had designed the University Club, to design the addition, on 36th Street. The building is stately – one may say too stately. Its austere facade led neighbors to call it “Morgan’s mausoleum.” Nonetheless, it is as finely wrought, both outside and in, as any building in Manhattan. The interiors have a baronial sumptuousness that the exterior lacks. Just now, however, one can’t visit the interior.

When Morgan died, he left instructions that, upon his widow’s death, his brownstone house was to be replaced by a building harmonizing with the library. The two buildings would then form a public museum of Morgan’s books and manuscripts. Benjamin Wistar Morris designed the new structure (1927-28), a model of forbearance in adding to a great building. Later, the museum bought the old Phelps house.

Two years ago, the museum closed to undertake a vast expansion. A new building, by Renzo Piano, is taking form on Madison between the Morris building and the Phelps house. Mr. Piano’s modernist building is very different from Morris’s building in its philosophy of adding to the old.

The museum will reopen next year. Meanwhile, the old buildings are being restored. Lately, the old library on 36th Street has been made to gleam as none of us had ever seen it do. Over the years its Tennessee marble walls had become dingy. Now we may appreciate the care with which they were designed and built (including their mortarless construction) as never before, as we eagerly await the museum’s reopening.