The groundbreaking, iconoclastic science fiction author Philip Jose Farmer introduced us to the Wold Newton Family concept back in 1972 with Tarzan Alive, a biography of the man Edgar Rice Burroughs variously called John Clayton, Lord Greystoke, and Tarzan of the Apes. In Tarzan Alive, Farmer asserts that Greystoke was a real person, and that Burroughs greatly exaggerated Greystoke's exploits for his pulp adventure audience.
In Tarzan Alive, Farmer did several things that set the tone for all Wold Newton works to follow. First, as noted, he followed the lead of Baring-Gould's 'biography' Sherlock Holmes of Baker Street and claimed that many fictional characters were in fact real people. Second, he analyzed the 'fictionalized' texts and attempted to reconcile any conflicting information, much as the Holmesian canon has been scrutinized for lapses in continuity by Baring-Gould, the Baker Street Irregulars, and others. Lastly, Farmer created the concept of the Wold Newton Family - a grouping of fictional characters that Farmer claims are blood related, including Tarzan, Holmes, the Scarlet Pimpernel, Raffles, Professor Challenger, the Shadow, and many others. He also accounts for the prodigious talents of Holmes, Tarzan, etc. by revealing that they are descended from a group of people traveling by coach in Wold Newton, Yorkshire, England in 1795 when a meteor struck a nearby cottage. The passengers of those coaches were exposed to radiation from the meteor, and this accounts for the benevolent mutations of their offspring (the Wold Newton meteor strike actually did occur on that date). Of course, their offspring all intermarried, and things became very complex.
Farmer continued to explore these ideas in Doc Savage: His Apocalyptic Life, a 'biography' of the classic pulp hero. Not only does Farmer further the conceit of the hero being a real person, but he adds many branches to his Wold Newton family tree. By the end of DS:HAL, we see a huge family of extraordinary folk emerging, from the Spider, James Bond, and Fu Manchu, to Leopold Bloom from Ulysses, Vonnegut's Kilgore Trout, and Farmer's own hero Kickaha from his World of Tiers series - among many others. Farmer adds more outre texts (from Lovecraft's Cthulhu Mythos to Harlan Ellison's talking dog Ralph von Wau Wau) than in his previous work and doesn't claim they are fictionalized to the degree asserted in TA.
Now, many years later, comes this superb volume edited and including work by Win Eckert, who has maintained the premiere site for Wold Newton speculation on the Web. Eckert has coined the term 'Wold Newton Universe' to denote that many more fictional characters than dreamed of by Farmer inhabit the same shared universe. Eckert has added many characters by documenting crossovers between fictitious characters from all media, in all genres, though the pulp theme remains strong. Eckert explains how the WNU 'works' and his own methodology in Myths for the Modern Age. Dr. Peter Coogan contributes an amazing essay, 'Woldnewtonry', which describes the way various writers 'wold', that is bring in more characters and reconcile more contradictory texts. There are many essays here by 'post-Farmerian' writers, such as Chuck Loridans, who reveals which female adventure characters are the 'Daughters of Greystoke'; Brad Mengel, who explores the tangled family tree of Sherlock Holmes; and Dennis Power, who discusses 'Asian Detectives in the Wold Newton Universe', brings Kipling's Mowgli into the Wold Newton Family in an interesting way and provides, with co-writer Coogan, a definitive look at the long and storied life of Burroughs' John Carter of Mars (which is timely what with a feature film on John Carter in pre-production).
I cannot recommend this book highly enough to any and all fans of Philip Jose Farmer, pulp heroes, Tarzan, Holmes, or crossover fiction such as the League of Extraordinary Gentleman (for which MFTMA contributor Jess Nevins has penned two exhaustive companion volumes). You may not agree with all of the theories about your favorite genre characters and the connections between them (just as in real scholarship, the 'parascholarship' employed here invites a wide range of sometimes conflicting theories - attempting to reconcile them into a cohesive universe is one of the many thrills of 'The Game'). But you will definitely have an incredibly entertaining and informative read.