Marvel Comics' big summer Spider-Man storyline, "New Ways To Die", promises to introduce a new villain into the webslinger's life: a mysterious character connected to his enemy Venom, called Anti-Venom. The most recent issue of Marvel's Fantastic Four series featured Mr. Fantastic stopping an invincible foe by wearing his new "Anti-Galactus suit". Sensing a trend here? We've got the full back story on this new anti-zeitgeist.
This isn't the first time that comic characters have had to face their opposites, although it's mostly been a DC schtick; Superman's imperfect clone Bizarro does everything Superman does backwards, after all, and the Flash has had a Reverse-Flash to deal with for decades, now (There's even a Legion of Super-Villains for the Legion of Super-Heroes). It's not even the first time that a villain has used the "Anti-" prefix (Who can forget Crisis on Infinite Earths' Anti-Monitor, who outlasted the Monitor by about two thirds of the series?). But Marvel's latest version of this idea may have less to do with exploring the undersides of villains' identities and more to do with exploiting brands for cheap identification - Fantastic Four's Anti-Galactus was a one-time appearance with no connection to the series' giant planet-eater beyond the name, after all. As to who and what Anti-Venom turns out to be, that's still shrouded in mystery for the most part, with Amazing Spider-Man editor Steve Wacker playing dumb when asked to elaborate:
[He's a b]rand new [character]...but he does have a tie to an existing villain in Spidey's life.
Gee, do you think that villain could be Venom? (The current and former Venoms have already been announced to be appearing in "New Ways To Die"; current speculation is that the original Venom, Eddie Brock, will turn into the Anti-Venom.)
For a more in-depth dichotomy between hero and villain, maybe you should be looking to The Sentry, Marvel's Superman clone who happens to be his own worst enemy… literally. The Sentry's arch-nemesis, The Void, happens to be the evil side of the Sentry's schizophrenic secret identity, Robert Reynolds, split into his own, separate, body. I could explain exactly how that works, but all you really need to know is, "Hey. It's comics." That whole "man versus his own dark side" thing is much easier here; even Captain America is doing it (Give it two months, and one of them will be calling himself the Anti-Cap).