Ace Books is infamous for their unauthorized United States publication of The Lord of the Rings.
In 1965 Ace Books discovered a copyright loophole in the American edition of The Lord of the Rings by J.R.R. Tolkien. The Houghton Mifflin edition had been bound using pages printed in the United Kingdom for the George Allen & Unwin edition. This placed them outside of U.S. copyright law as it stood at the time. Exploiting this loophole, Ace Books published the first ever paperback edition of Tolkien's work, featuring cover art and hand-drawn title pages by Jack Gaughan which, startlingly, depicted a lion in (presumably) The Shire. After considerable controversy and the release of a competitive, authorized (and more complete) edition by Ballantine Books, Ace agreed to pay royalties to Tolkien and let its still-popular edition go out of print.