He was the author of five novels featuring the vampire Don Sebastian de Villanueva, a cynical, amoral and misanthropic Spanish nobleman whose predatory appetites pale into insignificance compared with the historical catastrophes which he witnesses in his periodic reincarnations. These are: the Inquisition in The Black Castle (1978); the Spanish conquest of the Aztecs in The Silver Skull (1979); and the French Revolutionary Reign of Terror in Citizen Vampire (1981). In the later novels Yellow Fog (1986, revised 1988) and No Blood Spilled (1991), Sebastian is resurrected in Victorian London and India, where the horror of his vampirism is again contrasted with non-supernatural evil, now in the person of Sebastian's human enemy, Reginald Callender. A sixth (and presumably final) Don Sebastian novel set in Tibet and entitled White Demon was planned and is advertised by some sources as being available for purchase, but in fact was never completed: Daniels had begun writing it before abandoning it due to the demands of his non-fiction projects and was told when able to resume that his publisher had lost interest.
Daniels also worked with the historical fiction genre. The Black Castle features appearances by Torquemada and Columbus; in The Silver Skull Sebastian confronts Hernán Cortés; in Citizen Vampire he has a couple of friendly encounters with the Marquis de Sade; and Madame Tussaud makes an appearance in Yellow Fog.
Daniels described his works as "tragedy, in which evil consumes itself", as opposed to the melodrama of most contemporary horror novels, in which "customarily good guys meet bad guys and win in two out of three falls". He cited Robert Bloch as an influence on his sardonic style, and was an enthusiast of the works of John Dickson Carr, who in several of his own works combined historical fiction with horror and the detective story.
Daniels was also the author of Comix: A History of the Comic Book in America (1971) and Living in Fear: A History of Horror in the Mass Media (1975). According to Daniels, at the time he wrote Comix, "there was very little literature on the subject and, in fact, there was very little being produced by fandom. It was an attempt to say, 'Look, here's what has been done in the medium.' I didn't sit down and talk to creators at great length or anything like that." Both Comix and the more extensively researched Five Fabulous Decades of the World's Greatest Comics - Marvel (1991) were written with a general audience in mind, in the hopes of educating both comic book fans and those unfamiliar with the medium.
Don Sebastian de Villanueva
- The Black Castle (1978)
- The Silver Skull (1979)
- Citizen Vampire (1981)
- Yellow Fog (1986; revised and expanded edition 1988)
- No Blood Spilled (1991)
- White Demon (started circa 1991 but never completed)
- Comix: A History of the Comic Book in America 198 pages, 1971, Random House, ISBN 978-0517110379
- Living in Fear: A History of Horror in the Mass Media, 248 pages, 1975, Charles Scribner's Sons, ISBN 978-0684143422
- Marvel: Five Fabulous Decades of the World's Greatest Comics, 287 pages, 1991, Harry N. Abrams, ISBN 978-0810938212
- DC Comics: Sixty Years of the World’s Favorite Comic Book Heroes, 256 pages, 1995, Bulfinch, ISBN 978-0821220764
- Superman, the Complete History: The Life and Times of the Man of Steel, 192 pages, 1998, Chronicle Books, ISBN 978-0811821629
- Superman: Masterpiece Edition, 96 pages, 1999, Chronicle Books, ISBN 978-0811821117
- Batman The Complete History: The Life and Times of the Dark Knight, 208 pages, 1999, Chronicle Books, ISBN 978-0811824705
- The Batman Masterpiece Edition: The Caped Crusader's Golden Age, 96 pages, 2000, Chronicle Books, ISBN 978-0811827829
- Wonder Woman: The Complete History, 96 pages, 2000, Chronicle Books, ISBN 978-0811831116
- Wonder Woman: The Golden Age, 80 pages, 2001, Chronicle Books, ISBN 978-0811831239
- The Golden Age of DC Comics: 365 Days, 744 pages, 2004, Harry N. Abrams, ISBN 978-0810949690
- Thirteen Tales of Terror (1971; with Diane Thompson)
- Fear (1975)
- Dying of Fright: Masterpieces of the Macabre (1976)
- New York Times obituary
- Daniels, Les. The Black Castle (1978, Charles Scribner's Sons, NY), jacket bio.
- Stephen Jones, ed. (2004). The Mammoth Book of Vampires. London: Robinson. p. 484. ISBN 0-7867-1372-0.
- Ward, Kyla (1995). "Living With Fear". Tabula Rasa. Retrieved 2009-07-19.
- Daniels, Yellow Fog (1986), author's introduction
- S. T. Joshi, "Les Daniels: The Horror of History" in The Evolution of the Weird Tale (Hippocampus Press 2004), p.166.
- Les Daniels, Historian of Comic Books, Dies at 68
- Novinskie, Charles S. (February 1992). "Les Daniels". Comics Interview (105) (Fictioneer Books). pp. 5–17.