I've blogged before about Philip Jose Farmer's 'Wold Newton Family' but in case you missed that one I'll explain again. Wold Newton is a spot in Yorkshire County in England where a meteor struck in 1795. (A true event.) At the time that the meteor landed, two large coaches, containing fourteen passengers and four coachmen were passing by. (A fictional event.) The radiation from the meteor changed the genetic structure of these passengers who went on to be the ancestors of most of the fictional supermen of the next several decades, including Tarzan, Doc Savage, Sherlock Holmes, Nero Wolfe, Captain Nemo, and many others. Thus most of the pulp characters and heroes of popular fiction are related and owe their super human mental and or physical abilities to the Wold Newton event. This has become a sort of huge game played by writers and artists ever since Farmer introduced the idea. For more about it, see Win Scott Eckert's exhaustive Wold Newton site. http://www.pjfarmer.com/woldnewton/Pulp.htm
Beyond the Wold Newton Family there is the Wold Newton Universe. This parallel reality includes all the fictional characters who aren't necessarily part of the WN Family but who exist in the same reality. For instance Jonathan Dark, the protagonist of Lin Carter's Jandar of Callisto novels. While I was doing the research I mentioned below on Farmer's Tarzan related work, I noted the bit on Win's page about Jandar. Now since a parallel universe version of myself had met Jandar of Callisto in Secret masters of Callisto, my novella sequel to Carter's series, I wondered if that meant I had joined the Wold Newton Universe. I emailed Win, and he said, yep, I'm in the WNU. And if you've ever appeared in one of my stories, so are you.