The Boys' Billy Butcher learned how to defeat his hated enemy, the Homelander, when he killed his very first 'Supe' at the beginning of his career. Back then, Butcher realized that eyes, mouth, and open wounds are the only weak spots for invulnerable superhumans, and he applied this lesson in the most brutal way when he finally killed his worst enemy.
In the comics, Billy Butcher is a man with one single purpose: to kill Homelander to get revenge for the rape and death of his wife Becky. Compared to The Boys TV show, where Butcher's behavior and motivations are more variable, in the comics, everything he does is to follow his obsession. Like other survivors of Supes-caused incidents, Butcher was recruited by the CIA officer Gregory Mallory as the first member of his team, The Boys, created to watch over dangerous superhumans. Mallory told Butcher the truth about his wife's death, and that he could teach him how to get his revenge on Homelander, even if it would take years. As part of his training, Billy's first mission (shown in The Boys: Butcher, Baker, Candlestickmaker #5) involved killing a group of Supes living in a large cabin in the woods. Using his military training and skills, Butcher kills everyone with ease, including an unnamed Supe with impenetrable skin.
During the incredible and climactic conclusion of The Boys, the Homelander goes insane after learning that his teammate Black Noir is actually a clone of his, created by Vought American to control and, if necessary, kill him. Black Noir, however, is deranged, and he committed numerous atrocities over the years (including raping Becky Butcher), posing as the Homelander. In The Boys #65, by Garth Ennis, Russ Braun, John McCrea, Keith Burns, and Tony Avina, the Homelander, who has just killed the President of the United States, fights against Black Noir inside the White House. Only Noir survives and emerges, wounded, to the outside, where he finds the U.S. Army waiting for him. Billy previously told the soldiers to aim for eyes, mouth, and open wounds, and then finishes off Black Noir by levering his head open by putting a crowbar in his eye socket.
Butcher's First Supe Kill Already Shows His Deadly Obsession For The Homelander
It's really significant that the way in which Butcher finally takes out the object of his hatred is very similar to how he killed his first Supe. It's a mark of how horrifyingly capable Butcher is that, even in his initial kill, he's observing the weaknesses of his enemy and taking note of everything he can use to take down his real target. In fact, this also explains why Butcher actually hates Supes. Every Supe that Billy kills over the years is just a proxy for the Homelander, a learning experience, a small stepping stone towards his ultimate goal. However, in the end, his obsession has become so great that not even the death of Black Noir and Homelander is enough, and Butcher unveils his real plan to kill every single person with Compound V in the world, including his friends.
Billy Butcher is a man trapped by his instincts, forced to perpetuate a cycle of violence, and the fact that his first Supe kill mirrors so closely his final revenge against the Homelander proves that, behind its gory and bombastic appearance, The Boys hides a really complex and masterfully crafted narrative.