Most definitely Night Fist from Hitman.
I can make a few but I’ll go with Joker.
Hardcore in what way?
You can have Thomas Elliot, Hush, who straight up kills people sews himself a new face and performs surgery on himself a multitude times.
Or maybe Psycho Pirate, or The comedian, or Black Hamd or even The Batman who laughs… it depends on your definition of “hardcore”
superboy prime is pretty hardcore
Me Ambush Bug duh
Wait, but what if Continuity is the most hardcore DC character?
Lobo, redhood
Anybody with the last name Gordon. that goes for Barbara Gordon, James Gordon, and James Gordon Jr.–all in different ways.
We all know Wild Dog could be the most hardcore DC character if someone gave him the Punisher MAX treatment.
The Spectre because his sad story of being murdered as a police officer, but he comes back from the dead to punish those who are guilty even in the little of things. Which this can be intense for some, but is absolutely awesome to people like me. I’d love to cosplay as this guy sometime!
Red Hood is my boy
The Main Man without question just my opinion Lobo
Dr. Manhattan gives zero fucks unless he wants to. After him, Superboy Prime, Ultraman, Doomsday, Darkseid, Mongol, and oh Black Canary for mind wiping Batsy (hardcore=mind wiping your own teammates to cover yours and everyone elses ass)