Christopher Tolkien, who edited and published the posthumous works of his father, Lord of the Rings writer JRR Tolkien, has died aged 95.
The news was confirmed by the Tolkien Society, which described him as "Middle-earth's first scholar".
After his father's death in 1973, Mr Tolkien published the acclaimed work The Silmarillion.
Scholar Dr Dimitra Fimi said the study of JRR Tolkien "would never be what it is today" without his input.
Christopher Tolkien was born in Leeds, and grew up in Oxford.
After serving in the RAF during World War Two he became a lecturer in Old and Middle English and Old Icelandic at Oxford University.
Christopher Tolkien edited and released The Fall of Gondolin in 2018
JRR Tolkien made a huge impact on fantasy writing with The Hobbit and The Lord of the Rings
He drew the original maps of Middle-earth seen in The Lord of the Rings books released in the 1950s.
He later became the literary executor of the Tolkien Estate, completing using his father's material from 70 boxes of unpublished work.
Tolkien Society chairman Shaun Gunner said: "Christopher's commitment to his father's works has seen dozens of publications released... we have lost a titan and he will be sorely missed."
Dr Fimi said: "From editing The Silmarillion to the mammoth task of giving us The History Of Middle-earth series, he revealed his father's grand vision of a rich and complex mythology.
"He gave us a window into Tolkien's creative process, and he provided scholarly commentary that enriched our understanding of Middle-earth."
Charlie Redmayne, HarperCollins UK CEO, described him as a "devoted curator of his father's work" who spent decades "bringing Middle-earth to generations of readers".