Its no secret that The Boys is intentionally drawing parallels between its primary protagonist and primary antagonist: Billy Butcher and Homelander respectively. The two are opposite sides of the same coin in a lot of ways, even though they fight against each other at almost every opportunity. Both had similarly traumatic upbringings, they both had a relationship with Rebecca and her son Ryan, and they both hate the other's kind to such a degree that it informs their actions at multiple points during the show.
Beyond this, however, it's clear that the two characters are fated to kill each other by the end of the show. Making them so similar to each other enhances the drama and adds a layer of tragedy to the show that it would be somewhat lost without. The similarities between Butcher and Homelander are difficult to miss, particularly in later seasons.
6 Both Genuinely Care for Ryan
The third season of The Boys has really driven home the idea that both Butcher and Homelander care for and want to be a father figure to Ryan. Even in the season finale, the two momentarily team up to fight Soldier Boy after he tries to kill the kid. Butcher attempts to keep his promise to Rebecca, though, like Homelander in Season 2 of The Boys, he messes up and unwittingly drives the boy into the arms of his enemy at the end of Season 3. This results in a reversed ending in which Ryan leaves with his father, rather than Butcher.
Homelander himself does genuinely care about Ryan. In fact, he seems to be the one thing that Homelander does truly love other than himself. He does not abuse the boy at all and seems tapped into his fear and loneliness, as those are feelings he more or less inherited from Homelander. In a twisted sort of way, he just wants his son to be free of his pain.
5 Mirrored Upbringings
Homelander and butcher were both raised to be tough and merciless. Neither had proper father figures in their lives, as the former was raised in a lab by doctors like Dr. Jonah Vogelbaum attempting to build a weapon, while the latter's father, Sam Butcher, was an abusive drunk who simply wanted to inflict pain on his children to make them "hard."
Looking back, it's clear how much their upbringings affected them in adulthood. They're both violent and toxic men who are willing to do whatever it takes to defeat their enemies, even at the cost of their allies at times.
4 Similarly Bigoted Worldviews
While Homelander harbors a significant amount of contempt for normal humans (especially his own humanity that he desperately wants to destroy), Billy Butcher instead has an intense hatred for all superheroes. Homelander hates humanity and considers himself above the so-called "mud people" due to his fear and hatred of weakness, which he identifies as a human trait.
Butcher, on the other hand, grew to hate superheroes after losing Rebecca, seeing them as inherently immoral freaks who abuse their power simply because they can, which is something he experienced as a child while being abused by his father. Both are partially (if not mostly) motivated by this hatred of the other, using it as justification for their actions against one another.
3 Both are Willing to Murder
People die in The Boys. In fact, a lot of people die on the show, sometimes in horrible and extremely bloody ways either from normal people or the various superheroes. Homelander and Billy are similar in that they have both taken lives, they've done it willingly and, sometimes, with a certain amount of glee.
Homelander has easily killed more people than Butcher has, killing the mayor and his son, a whole plane full of passengers, random criminals, terrorists, and many many more. Butcher, on the other hand, is either directly or indirectly responsible for the deaths of several superheroes, Vought employees, soldiers, and criminals, both with powers and without. Though Billy claims to hate using his powers to kill, there are times when he revels in it, much like Homelander does.
2 Powers and Abilities
When Butcher takes the Temp V drug in Season 3 of The Boys, he is granted superpowers for 24 hours. These powers include super strength and durability, as well as powerful laser eye beams. These are some of the same powers that Homelander possesses, a fact that is highlighted in the fight between him, Butcher, and Soldier Boy.
Butcher can't fly and it's not yet known if he has X-ray vision or super hearing, but he does have enough of the same powers as Homelander that he is able to actually engage him physically and not only survive, but potentially best the superhero. The fact that Butcher is willing to turn himself into a Supe to accomplish his goals is a great source of conflict for him. He has always hated superheroes and their power, and yet he's willing to become what he hates if it means he finally gets to kill them.
1 Willing to Use Others for Their Agenda
As the leaders of their respective teams, Homelander and Butcher rely on their teams to back them up many times but are also willing to use them for their own ends. Homelander repeatedly abuses his authority over the rest of The Seven, especially when it concerns public perception of him, the team, and Vought. He also does this when it furthers his plans, such as in Season 3 when he orders The Deep to eat his octopus friend Timothy, or when he forces Starlight to appear as his girlfriend.
Butcher occasionally does something similar, though not to the same degree. For example, Butcher repeatedly uses Hughie as either bait or as an unwitting accomplice in his self-destructive plans. He also took advantage of Frenchie and his connection to Little Nina in order to get to Russia, which caused problems of its own for the group.