Demon in a Bottle and Extremis. Still, most heroes have a couple of duds in their history, especially when they've been around for decades on end. However, the introduction of Anthony Stark remains one of the most wrong-headed and maligned stories in comic book history.
There was an ongoing trend in the '90s to replace popular comic book mainstays with younger, edgier counterparts. Peter Parker was replaced with Ben Reilly during The Clone Saga. Jean-Paul Valley briefly became Batman in Knightfall. Superman was temporarily replaced by four would-be successors after his death. Iron Man also underwent a similar recasting, albeit in an extremely odd and convoluted fashion.
The story starts with Avengers going back in time after Tony Stark was pushed to the dark side by the influence of Immortus, which now has nipples for some reason. He enrolls in college as Anthony Stark, denying any relation to the genius billionaire playboy philanthropist. He also sees Meredith McCall, his former girlfriend turned college professor and fights several villains.
While Anthony Stark's tenure as Iron Man was short-lived, his ending was just as convoluted as his beginning. Anthony seemingly perished with the rest of the Avengers and Fantastic Four in the fight against Onslaught. In actuality, they were transported to the Heroes Reborn pocket dimension (itself yet another attempt to revitalize the Marvel heroes, this time with Image creators). Upon his return, Franklin Richards merged Anthony with his not-quite-dead older self, finally putting an end to this bizarre chapter of Iron Man lore.
With Tony Stark dead in the current Marvel Cinematic Universe, the storyline does provide an interesting blueprint on how Marvel could recast Tony with a different, younger actor if they wanted, especially given how time-travel supposedly works in the MCU. There are some interesting emotional beats in the storyline, such as the younger Tony's relation with now-older friends like Meredith and James Rhodes. On the other hand, the much-maligned story dramatically illustrates the pitfalls of trying to revitalize a popular character for a new audience. Apparently "if it ain't broke, don't fix it" also applies to Iron Man.
