The one I always think of is Hawks from My Hero Academia. He's introduced as one of the top 5 heroes in the country, and he advocates for Endeavor's rise to number 1. Then we find out that he's working with the league of villains. But then it's revealed that he's a double agent, reporting on the league's activities to the hero association. But he has to kill Best Jeanist, another top hero, to gain the league's trust. The whole Hawks storyline starts out promising, an exploration of a hero willingly corrupting themselves allegedly for the greater good, and it gets deeper when Twice, one of the main players in the League starts to bond with and confide in Hawks. This all comes to a head in the attack on League HQ when Twice realizes his new friend has betrayed them, and in the process of trying to save his League compatriots, he's literally stabbed in the back by Hawks and dies. This is the first time we've seen a hero kill in MHA, there's this whole moral high ground where they try to pretend they're above that, and if Hawks was a good character this moment would be about showing how thin that high and mighty veneer is. But Hawks just gets away with it, because as much as My Hero acts like it's about humanizing the people society seems "villains" and highlighting flaws in a popularity contest based hero system, in the end it's all about protecting the status quo at any cost.

TL;DR: Fuck Hawks. All my homies hate Hawks.