Jax Augustus was first mentioned in Chapter Four and then again in Chapter Five. Actually, twice in Chapter Five. And I have a nagging feeling I’m overlooking another mention, too. He’s a little bit like a running gag in this comic (apart from not actually being funny). EDIT: It turns out I missed a whole bunch of Jax references, including getting his first “appearance” wrong. *blush* See the comments below for further details.
If you’re interested in re-reading Carl’s story about what happened to the Hiawatha, it begins here.