Random Encounters

[DHBirr]

Reviewing the ATT entry for Jenny Everywhere, I was reminded that Christopher Stasheff wrote something similar about his character Rodney d'Armand a.k.a. Rod Gallowglass of The Warlock in Spite of Himself:  he seems to be a very high-probability person, and the version of him in the interstellar future that's the series' main setting is more-or-less identical to the one in a completely magical universe where "science never had a chance to grow."  Another character assesses that there probably isn't a variant of Rod in any world that never developed humans "—but I wouldn't want to guarantee it."  

Incidentally, Rod's alternate in that far-away universe had still scored a wife who was just as almost-identical to Rod's Gwendylon (no; I didn't misspell her name). 

Edit:  Another possibility is L. Sprague de Camp's Harold Shea, possibly accompanied by his wife and/or by some of his fellow psychologists, inserting into lots of fantasy tales.  Why shouldn't there be one in which Shea meets a strange fellow riding a weird motorcycle?

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Up, lad, up!  We've villages to pillage, maidens to slay, and dragons to rescue!