Iron Man needs a new arch-foe and Marvel has the perfect one already.
A hero as iconic and beloved as Iron Man deserves a true arch-nemesis he can match wits with, and the perfect candidate can be found in the Marvel Cinematic Universe's next major villain: Kang the Conqueror. Thanks to the wonderful performance of Robert Downey, Jr, Iron Man skyrocketed in the public consciousness from C-list superhero, launching the Marvel Cinematic Universe into the stratosphere. Nevertheless, even after this meteoric rise at the box office, the Golden Avenger still struggles in comic sales. Superheroes with the kind of movie money that Iron Man pulls in such as Spider-Man and Batman will often have multiple series running at the same time. Poor Tony however struggles to maintain even one book at a time to this day. One possible reason is that the character lacks a marquee level arch-nemesis. By doing a little bit of shuffling, Marvel could easily rectify this.
While Downey was able to draw in audiences through sheer force of charisma and wit, even the popular MCU version of Iron Man struggled to find a good threat to match his charm. Obadiah Stane, Whiplash, Aldritch Killian, and even Ultron each went over like a dull thud. It took Thanos himself before audiences felt like Tony had a villain equal to his stature. Comic fans might protest, citing the Mandarin as Tony's big enemy. The Mandarin might have worked in the days of the Cold War but has grown stale, leaving a hollow stereotype with too much culturally problematic baggage. Even the MCU struggled to actually use him, finally transplanting him over to Shang Chi's movie and making him entirely different from the comics. The rest of Tony's villains are either too bland (Whiplash, Blizzard) or too niche (Ghost, Spymaster) in motivation to work as an arch-foe for Iron Man.
In reality, the perfect foe for Iron Man already exists in the Marvel Universe and is ironically set to become the new main threat of the MCU in the wake of Tony's cinematic death. Marvel should turn Kang the Conqueror into the new arch-enemy for Iron Man in the comics. Much of the groundwork has already been laid for the two to be immensely personal enemies. Kang debuted in Avengers #8 by Stan Lee and Jack Kirby, with Iron Man a mainstay of the team. In the 1990s, one of Tony's biggest blows happened when Kang brainwashed him into being a mole in the Avengers. Furthermore, as a conquering tyrant with vast resources and weapons from the far future, he serves as more than a threat to Iron Man's ever-evolving technology.
Most importantly, Kang is the antithesis of what Iron Man is: a man from a utopian future who goes back in time to wage war as a hobby. He is a repudiation of Tony's futurism philosophies, a rejection that mankind can process and improve through technology. This is even something Brian Michael Bendis already noted during his Avengers run. Whereas writers could never really nail down a solid characterization for the Mandarin that could justify him being Tony's main villain, Kang could be an evergreen nemesis for Tony. Kang seeing Iron Man's futurist ideals as a personal offense to his warring ways and vowing to sabotage them almost writes itself.
With Kang as the new main villain for Iron Man, writers could maybe stop trying to do "Iron Man's worst enemy is himself" stories over and over again. Saturation of that idea will ruin the character. Instead, it might be a better idea for Iron Man's goals to improve humanity being things that could actually improve humanity with Kang the Conqueror as his foil. As Kang stands ready to be the main threat of the MCU going forward, he stands as the best opportunity for Iron Man's incredible MCU success story to be repeated in the comics.