Out of all the plot twists in comic books, Young Avenger's member "Iron-Lad" was at the center of one of the best, and tragic, plot twists.
In the aftermath of 2003's "Avengers Disassembled," where Scarlet Witch lost her mind and was responsible for the deaths of several longtime Avengers (such as Hawkeye and Scott Lang, Ant-Man), the Avengers were no more. In their wake, a new team of superheroes rose from the ashes, dubbed the "Young Avengers" by the press, and began to fight crime in their stead. The initial line-up consisted of Patriot, Elijah Bradley, grandson of The Original Captain America, Hulkling, the Kree-Skrull son of the original Captain Marvel, Wiccan, one of two sons that Scarlet Witch had, and Iron Lad. Though the team attracted the attention of Captain America and Iron Man, two Avengers who did not like the idea of teenagers putting their lives at risk, they were determined to band together and stop a coming threat in place of their predecessors. However, When Captain America, Iron Man, and Jessica Jones (who had been tasked to find the Young Avengers at the behest of her employer, J. Jonah Jameson), confronted Iron Lad, they were shocked to learn his true identity: Kang the Conqueror.
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Kang the Conqueror is a time-travelling villain from the future, and one of the Avengers greatest foes. During one of his journey's through time, Kang encountered a younger version of himself being bullied, specifically by a boy who would put Kang in the hospital and ruin his family financially. The elder Kang showed the younger one all of their future exploits together, and that the two of them would become great despite the Avengers constant meddling. Though Kang gave his younger self a version of his own power armor, as well as the opportunity to strike down his bully, the young Kang rebelled, and fled to the 21st Century, with the hope of enlisting the Avenger's aid in preventing himself from turning into the evil Kang.
However, when he arrived, the Avengers had already disassembled, which led Kang to track down data on their whereabouts himself. Kang would, after breaking into an Avengers tech vault, find the remnants of the Vision (another Avenger who fell during Wanda's breakdown) and, upon downloading his memories into his armor, would discover a fail-safe plan that would lead him to younger heroes that could replace the Avengers in the event the team fell, and would then form the Young Avengers.
After explaining the situation to Captain America, Iron Man, and Jessica, while they initially planned on helping Iron-Lad, realized that sometimes, one cannot escape fate. When the older Kang arrived in the present day, looking to return Iron-Lad to his place in the timeline, he was initially met with fierce resistance. However, the timeline slowly began to change, with New York being destroyed and Jessica Jones reverting to her Jewel identity. Kang explained that, the longer that Iron-Lad stays in the present, even if he managed to avoid turning evil, the timeline itself would change drastically as Kang himself is integral to the Avengers history. The Young Avengers intervened, and tried to keep their friend from accepting his fate, with Iron-Lad even killing his future self. However, as the timeline changed even more, Iron-Lad realized that he would have to return to the future to ensure that his new friends would not disappear forever. Using a version of the Vision present in his armor, Iron-Lad managed to wipe his memory clean, and return to the exact moment in time Kang plucked him from. While Iron-Lad would then go on to become the villainous Kang, his story was far from over.
As it turned out, Iron-Lad's brainwaves remained in the Iron-Lad armor that, when mixed with the Vision and his A.I., became a brand new person, a "Young Vision" of sorts. While this new Vision remembered bits and pieces of his time as Iron-Lad, specifically his friends, he was essentially a brand new person. However, this new Vision was not initially accepted by all, and was supervised by Tony Stark and the Avengers as, because the Iron-Lad armor was initially Kang's, there was a chance Vision was evil. However, after helping the Young Avengers prevent another Kree-Skrull war from breaking out, Vision became a full fledged member of the Young Avengers. Vision would also form a romance with Stature, Scott Lang's daughter and member of the Young Avengers, and even join the Mighty Avengers for a period of time.
Though the original Iron-Lad has made appearances over the years, and the original Vision has returned to his older personality, Iron-Lad's initial appearance was still memorable, and tragic. For years, Kang had been a major villain in the Marvel Universe, seeking conquest and power at any cost. Iron-Lad made Kang a tragic character, one who rejected his villainous fate and tried to live a better life as a hero. However, the young Kang could never have such a life, as doing so would result in the destruction of history as we know it. Kang the Conqueror, unintentionally and with no memory, actually became one of Marvel's greatest heroes, opting to surrender a life of heroism and happiness for the safety of his friends, and the rest of the world. Iron-Lad as we knew him may be gone, but his legacy of heroism will certainly not be forgotten.