Philosopher of Evil: The Life and Works of the Marquis de Sade by Walter Drummond aka Robert Silverberg (Regency Books, 1962)
In the 1960s, Silverberg was penning just about as much non-fiction as he was writing softcores, SF, and whatever else. He used a number of pen names, writing books for the YA and trade market in history, anthropology and oceanography, as well as a dozen sexual case histories and research as L.T. Woodward, MD (after the success of Masters and Johnson, publishers put out both real and fake sexology studies in droves).
As Walter Drummod, Silverberg wrote two curious titles for Regency Books: this biography of the Marquis de Sade, and one about how to invest and spend money wisely.
Regency Books was owned by William Hamling, part of the Greenleaf/Cornith arm, and edited by Harlan Ellison. Ellison published two of his early books with the imprint, Gentlemen Junkie and Memos from Purgatory. Interesting note: Regency originally published Jim Thompson’s The Grifters. Ellison did have an eye for what was good.
Philosopher of Evil is written for a general audience, not academic; too bad as sometimes we wished for sources of quoted material. But this was a quickie paperback meant to entertain and at times, excite with graphic descriptions of de Sade’s personal sex life and the depravity found in his novels.