Antagonists

“	Naturally, I'm very interested to know how you're able to commit these murders without being present, but I don't mind waiting a little bit longer. You can answer all of my questions when I catch you. Let's meet again soon... Kira.	„
	~ L antagonizes Kira during his TV broadcast.

“	Do you wanna have a bad time?	„
	~ Sans threatening Frisk in Genocide Route.

A heroic antagonist or antagonistic hero is a character who is in the opposition to the protagonist, yet is heroic in nature; this is usually due to the protagonist being a villain protagonist (e.g. L Lawliet, Sans, Tres Magia, Vincent Hanna, Hank Schrader, Swansea, Bryan Pawalski), but there are also conflicts where both the protagonist and the antagonist are heroes (e.g. Inspector Javert, Anxiety, Jiren, Squidward Tentacles, Miles Edgeworth, Byakuren Hijiri). In short, antagonist heroes are heroes who oppose the protagonist, whether good or evil.

It is possible for a hero to fall into both the false antagonist and this category if they antagonize the protagonists in early installments/story arcs but join their cause later in the story (e.g. Satsuki Kiryūin, Bee, Lori Spengler, Mr. Krabs, Michael Afton, Donkey Kong, Furina de Fontaine and Shadow the Hedgehog).

A friend/ally of the protagonist can also become a heroic antagonist, if the protagonist and the former breaks up due to different ideal (e.g. Suzaku Kururugi) or the protagonist is/becomes a villain and the former turns against them in opposition at one point of a story (e.g. The Judge).

Note:

This is for heroic (or anti-heroic) antagonists, not for reformed villains who were unambiguously evil when they used to oppose the heroes. Heroic Antagonists can only be redeemed villains if they were already at least partially heroic when they were villains before redemption. Characters who were originally villain antagonists without any heroic role shouldn't have this category here.
For obvious reasons, these characters are rarely Pure Good since it is not common in many works for an opposing character to actually be Pure Good, though there are some huge exceptions if they completely lack any corrupting qualities and the other characters are visibly pleased or comforted by their actions. It may also help if the protagonists of the story are villains. Mister Rogers, Soichiro Yagami, SCP-999, Falco Grice, Byakuren Hijiri, Spider-Man (MCU), and General Hubert Galeforce are good examples.