"Aztek: the Ultimate Man" by Grant Morrison, Mark Millar, and Others
Grant Morrison AND Mark Millar wrote this one. Yeah, the art inside is pretty bad, but I was hoping that the story made up for it.
I'm not up on Aztek's backstory, but apparently it has something to do with some secret, South American society that trains warriors for a coming showdown with an evil god. Every so often they elect a champion, and this champion wears a special helmet that allows him or her to use some kind of "fourth dimensional power." The power accessed is non-chronological in nature, so I'm thinking that the fourth dimension accessed must be something other than time.
Anyway, it's probably not worth thinking about.
Aztek spends this TPB adjusting to modern life, and having somewhat amusing conversations with other superheroes. It's not nearly as good as anything Morrison did with Animal Man, and light years away from Millar's work on The Ultimates. If it's not quite boring, it's not quite interesting either.