There's some mythology here, perhaps another J9 greybeard can answer. The story I've heard so far goes as follows...

There was some constant for 8K that was mistyped incorrectly, something like instead of:

#define 8K 8192

They mistyped and wrote:

#define 8K 8096

This caused all sorts of bugs and was known internally as the 8K bug. When time came to write the Java VM, they wanted to name it as "post 8k bug" they named it K9, but K9 sounds like a dog (woof) so they decremented the K to land on J9.

At least that's what I've heard...

shrugs

Here's the true story: https://medium.com/@rservant/how-did-the-j9-in-openj9-get-it...

This close, but not right. Dogs never entered into the equation. I'll post a blog somewhere with the history and come back here with a link.