Contains spoilers for The Boys comic book series
Throughout The Boys, Homelander is shown to be untouchable, as no matter who he fights or takes on, the Supe comes out on top thanks to his devastating powers. However, one Supe ended up breaking the leader of The Seven with a single punch, as Black Noir's final confrontation with Homelander led the latter to suffer like never before. The Homelander clone ended up completing his near-impossible mission and defeated the Supe he was created from in an absolutely horrifying way.
While Homelander has a powerful adversary in The Boys television series, as Soldier Boy is changed from his comic counterpart to have powers capable of stopping the out-of-control Supe, initially, he wasn't stopped until the very end of his story. No matter which Supe tried to stop Homelander, including Queen Maeve dying at his hands after trying to protect Starlight, nobody could even make him flinch. However, when Black Noir revealed himself as Homelander's clone and took him on as he completely lost control, he proved not only to be able to hurt the leader of the Seven but break him like no one else had previously.
In The Boys #65 by Garth Ennis, Russ Braun, John McCrea, Keith Burns, Simon Bowland, Tony Avina, and Darick Robertson, Homelander enacts on a coup on the United States, pushed on by blackouts during which he seems to be committing heinous crimes, including cannibalism. As a result, he kills the President of the United States as he welcomes the U.S. Military's attempt to stop him. But, when Black Noir arrives, it's revealed he was the one who committed Homelander's darkest crimes in an attempt to push him over the edge. The two clash in the Oval Office, and despite Homelander's fearsome reputation, the equally powerful Black Noir literally punches his bottom jaw off with his first blow in a moment sadly too gory to show here.
For the entire The Boys series up until that point, Homelander seemed physically impossible to break. Yes, he suffered emotional outbursts and pined for the approval of Vought executive James Stillwell, but even the other members of the Seven cowered before him. Black Noir broke Homelander physically and emotionally, showing that while Homelander was seemingly untouchable, he was utterly vulnerable to someone of comparable strength.
This moment seems to indicate that Homelander's strength actually far exceeds his invulnerability, as his clone's punch is so physically devastating, it's clear that the fight is nothing like two regular, evenly matched humans coming to blows. Homelander does his own damage to Black Noir, especially using his heat vision, but it's shocking that one punch was able to do such devastating damage - the type of damage that the series usually shows Supes dealing out to regular people. Even using her full strength, Queen Maeve was barely able to break Homelander's skin, despite being described as one of few beings even approaching his power level.
Homelander's vulnerability to his clone is an essential part of his death, as it shows that the seemingly unbreakable Supe is absolutely devastated in a fair fight. Homelander didn't earn his abilities or wield them with any particular expertise, holding dominion over others due to his inherently higher power levels. The punch that severs his jaw is therefore the first moment Homelander enters a fight without an overwhelming advantage, and he's instantly decimated. While some series would have depicted a titanic, 'Superman vs Zod' style struggle, The Boys' Black Noir vs Homelander fight acknowledges them for what they are - living weapons designed primarily for offensive power. That Homelander is immediately dealt such a bloody defeat emphasizes the power Vought has irresponsibly put in the Supes' hands, and shows that in the end, The Boys' big bad is nothing without an unfair advantage.