The Avengers is a team that is constantly evolving both in terms of the revolving door of active members as well as the growth in power and skill of the heroes on the team, however, one Avenger pushed himself a bit too far in the name of progress—one whose ultimate upgrade tragically became his greatest weakness.
The founding members of the Avengers first joined together as a team in Avengers #1 by Stan Lee and Jack Kirby, a team that consisted of Iron Man, Thor, Ant-Man, Wasp, and the Hulk. After only sixteen issues, however, the original team disbanded, leaving newcomer Captain America in charge of the Avengers. Then, Cap was responsible for leading the replacement heroes (who filled in for the founding squad members), and those heroes were Hawkeye, Scarlet Witch, and Quicksilver. While the original members weren’t called upon for every Avengers mission after their departure, they still made guest appearances from time to time if the situation was serious enough to warrant their involvement. When one founding Avenger returned, it's revealed that he had been making some serious upgrades to himself off-panel—ones that made his power exponentially more useful but with a side effect that proved deadly.
In Avengers #28 by Stan Lee and Don Heck, Hank Pym aka Giant-Man reaches out to the very team he founded for help in rescuing his wife Janet Van Dyne aka the Wasp from the evil clutches of the Collector. Of course, the Avengers jump into action immediately to help their colleague, but not before they put Hank through one specific test. In this issue, Hank didn’t approach the Avengers as Giant-Man, but as Hank Pym, and the Avengers didn’t know Giant-Man’s secret identity prior to this issue and needed to make sure Pym was who he claimed to be before trusting him. In between leaving the Avengers and returning to them for help, Hank had upgraded his growing and shrinking technique to the point where he didn’t need a special Pym Particle delivery system within his suit to activate his powers but could simply will himself to grow into a giant or shrink to the size of an ant. Unfortunately, the fallout of that upgrade nearly cost Hank his life, something the Avengers witnessed first hand.
Hank Pym turned his reliance on a suit into a legitimate, natural superpower, but that took a nasty toll on his body. As revealed in this issue when the other Avengers made Hank prove that he was really Giant-Man, Pym only had the ability to increase his size and couldn’t shrink anymore because shrinking would immediately destroy his body–this would effectively eliminate his Ant-Man persona. Plus, Giant-Man can only stay giant for 15 minutes, and his max height is only 25 feet. The irony of Giant-Man’s plight is absolutely tragic as right when he’s able to give himself the ability to use his powers without the need of a bulky suit—which would make him a much more effective superhero—his powers become too much of a danger to use, making his ‘upgrade’ absolutely pointless.
Even though there were many risks in Giant-Man using his powers to save the Wasp, Hank didn’t hesitate to join up with the Avengers and go on the rescue mission alongside them. During that mission, Hank stayed a giant for much longer than 15 minutes. After Janet was saved and he tried to shrink back down to normal size again, the transition nearly killed him–showing everyone first hand how truly perilous Giant-Man’s abilities had become and proving that this founding Avenger’s ultimate upgrade is also his greatest weakness.