[McMock]

Yup. Well done. I didn't know about this, and I've never heard of the The House of Mystery series. Cain himself is a cameo from the bible, as everybody knows, but the resemblance in how he's drawn is uncanny. I did not know you were dutch.

Hmm. In other issues where Neil Gaiman uses somebody elses character, he tends to mention where he got it from, though. Like in the episode with the woman who could change the fabric of her body (and the sungod), he mentions he got the character from, well, I don't remember the name of the series. And there are a few other occurances like that where he uses a character, but gives the author credit. Maybe he didn't feel like doing so with Cain because obviously the crecit for coming up with the character is not that of the author of The House of Mystery, but I wouldn't rule out that it's something the guy who drew the comics did, perhaps subconsciously, and that Neil Gaiman had nothing to do with it. (Because Neil Gaiman is only the writer, and doesn't decide how the characters look on paper. So it's impossible that his subconscious is to blame here)

Well found, nevertheless. Neil Gaiman has a blog and he answers questions from his fans who write him there. It's a very high traffic site, and I do believe he takes his fans seriously. Maybe you could send him an email with the scan and ask him if you really want to know.