From Jess Nevins, who gave an interesting presentation on similar stuff more recently (lecture on physical culture and its expression in literature; MP3, well worth the time -- I'm a huge Doc Savage fan, but had no idea that Eugen Sandow, the father of bodybuilding, had inspired dime novels), an old but fascinating glimpse at crossovers and at RPF for pay, back in the day.
Crossovers involving the use of fictionalized versions of real people became common in the last decade of the 19th century and the first decade of the 20th century. Celebrities have often been used by authors in their stories, but before the growth of the news media in the 19th century these men and women were the products of folklore rather than reality. Dick Turpin appeared in William Ainsworth's Gothic novel Rookwood (1834) and in penny dreadfuls, but the Turpin used in those works was a heavily romanticized version which bore little relation to the real Dick Turpin. The growth of the newspaper in the 19th century allowed individuals other than heads of state to become internationally known, and allowed them to be used by authors as supporting characters in serial fiction. Thomas Byrnes (1842-1910) was appointed Detective Bureau Chief of the New York City Police Department in 1880, and over the next fifteen years Byrnes turned the N.Y.P.D. into a modern, professional police force, one widely admired for its efficiency. Byrnes became a celebrity during these years and was seen as the personification of modern policing. He was incorporated into at least eight different dime novel detective serials in the 1890s as "Superintendent Byrnes" or "Inspector Byrnes," the "Head of the New York City Police Department" and the man responsible for giving Nick Carter or Broadway Billy or Dave Dotson or Gideon Gault their orders. Theodore Roosevelt, during the years of his presidency, was almost as popular a subject for appearances in the dime novels, as was the internationally renowned strongman Eugen Sandow (1867-1925). A fictionalized version of the Russian terrorist Evno Azef (1869-1918) fought the mystic Sâr Dubnotal in the French pulp Sâr Dubnotal and Sexton Blake in the British story paper Union Jack, both in 1909. A fictionalized version of the Japanese spy Oka-Yuma appeared as the enemy of Nat Pinkerton in the German heldroman (dime novel) Nat Pinkerton, der König der Detectivs in 1910, as the villainous lead in a serial, "Oka-Yuma, Japanese Spy" in a Russian newspaper in 1911-1912, and as the enemy of Lukas Hull in the German heldroman Lukas Hull, Detektiv Abenteuer in 1921.