Lathrop Colgate Harper (1867-1950) and Mabel H. Urner Harper (1881-1957), a socially prominent couple of early twentieth-century New York, lived for years on Gramercy Park and served as benefactors for some of New York's finest institutions. Their domestic lives and European travels were immortalized in the pages of over one hundred newspapers in the United States, Canada and Great Britain through Mabel Urner's syndicated, semi-autobiographical column, The Married Life of Helen and Warren.

Lathrop Colgate Harper was a successful rare book dealer, consultant to many major U.S. research libraries and authority on incunabula, Americana, and medieval manuscripts. A native New Yorker, Harper traced his lineage to several distinguished New York families. His grandfather, Samuel Barker Harper (b. 1777), married Christina Arcularius, daughter of New York Alderman and State Assemblyman Philip J. Arcularius. Harper's father, the tea merchant James Philip Harper, married Margaret Perego, daughter of a wealthy New York merchant whose family had settled in New Jersey by 1750. Harper was the great nephew of New York Mayor James Harper and second cousin of the Harper Brothers publishers.

In 1887 Harper joined his elder brother, Francis P. Harper, in the rare book business at 4 Barclay Street. The bookstore successively moved to 17 East 16th Street, 14 West 22nd Street, 437 Fifth Avenue and finally 8 West 40th Street. After his brother's early retirement in 1910, Harper developed his interest in Americana.. He became a much sought-after source of rare Americana after obtaining for William L. Clements the Americana library of Newbold Edgar, which would become the core collection for the William L. Clements Library at the University of Michigan. He was granted an honorary Master of Arts by the University of Michigan in 1928 in honor of his efforts in the library's development and subsequent growth. He was well known to many research libraries, serving on library committees for Harvard University, Princeton University, The New-York Historical Society and the Council of The Bibliographic Society of America, among others. In the 1920s, he developed an interest in incunabula (books printed before 1501) and went on to compile the first catalogue of incunabula published in the United States, A Selection of Incunabula Describing One Thousand Books Printed in the XVth Century (New York: 1930), once considered a basic reference resource.

In 1912, Indiana native Mabel Herbert Urner (1881-1957) married Lathrop C. Harper. She continued to use her maiden name in her professional life. She began a newspaper column in 1914, The Married Life of Helen and Warren, a fictional account that was based primarily on her life with Harper. The column was eventually syndicated in over 100 newspapers in the United States, Canada and Great Britain; it ran for thirty years, finally ceasing in 1944. The couple took yearly trips to Europe, during which Harper hunted for rare books and Urner combed markets for seventeenth and eighteenth century samplers, antique glassware, antique snuff tins, amber, furniture and other collectibles. Harper became known as a connoisseur and keen appraiser of rare books, and Urner developed collections to fill their Gramercy Park home that would eventually catch the eye of the national press and be bequeathed to the Metropolitan Museum of Art after her death. Her readers' queries about the couple's travels and interest in the cuisines of Europe eventually prompted Urner to write and self-publish a series of noncommercial but popular "Guidelets" on European travel and food, beginning in 1930.

In 1948, just two years before his death, Harper received an honorary Doctor of Arts degree from Brown University. The citation acclaimed his achievements and industry in helping to compile libraries across the nation, stating, "The shelves of the noblest libraries in this country reflect your zeal for letters and your discriminating love of books." He died in his office on August 11, 1950, his hand still holding the phone as he prepared to make his nightly call to his wife. Urner followed him in death on March 2, 1957, leaving behind thirty years of journalistic writing. Parts of the Harper estate were donated to New York area institutions including Princeton University, the Metropolitan Museum of Art and The New-York Historical Society.