Black Noir, turns out, was created to be stronger than the Homelander to keep him in check in case he goes rogue and needs to be put down.
The problem started when Homelander began behaving well, and Black Noir just assumed his spot in the Seven, along with the other super heroes. Years passed and it seemed Black Noir wasn’t going to be given the chance to perform his sole reason for being: kill Homelander. So he started doing things to mess with Homelander’s head and break down his psyche.
Black Noir did it by committing heinous atrocities and blaming it on the Homelander. How? Easy, since it was revealed that he was an insane clone of Homelander, he was able to pin the blame on Homelander by donning his costume.
From – The Boys #65