We now know that Folger First Folio 75 was owned in the mid-1600s by Constantine Huygens, a Dutch diplomat, poet, and humanist. (Today, he is even better known for his second son, Christiaan Huygens, a famous Dutch scientist and mathematician.) The association with Constantine Huygens, however, was not confirmed until the early 21st century.
Constantine Huygens purchased his First Folio in 1647, making it the earliest known First Folio to be owned outside of England. By the late 1700s, it was back in England, where it was eventually acquired by the banker Sir Coutts Trotter. Trotter died in 1837. He left the First Folio to his daughter Anne, who married into the Lindsay family, and it was owned by the Lindsays until 1925. Henry and Emily Folger bought it in 1928.
The confirmation that this was Constantine Huygens's First Folio—and that he purchased it in 1647—came in 2009 as the result of work by Dr. C.J. Verduin at the University of Leiden and Dr. Ad Leerintweld. Dr. Verduin noticed that the description of the First Folio in Anthony West's First Folio census includes the faint annotation "Constanter," which Huygens typically used to mark his books. New ultraviolet imaging at the Folger, which West helped to arrange, showed the word "Constanter" more clearly. Dr. Leerintweld knew that such annotations often included the year of purchase. He saw something unreadable just below the engraving and asked for an additional ultraviolet image, which revealed the year "1647."
The Huygens copy is unusually complete, including every leaf of the preliminary content and the plays. Someone has listed the characters at the end of several different plays, including Titus Andronicus, Julius Caesar, Macbeth, Hamlet, King Lear, and Antony and Cleopatra.