It could be Harry Potter himself. After realizing how he had been used, Harry might decide to hold Dumbledore accountable. Harry has the power and the motivation, having been through so much due to Dumbledore's actions or inactions.
In some interpretations, one possible crime could be his manipulation of Harry Potter. He knew Harry was a tool to defeat Voldemort from the start and perhaps didn't fully disclose this to Harry, leading Harry into a dangerous life without his full knowledge.
Well, Homelander is a complex and often self - centered character. If he were in an Avengers fanfiction, he might initially see the Avengers as a threat to his own status. He'd probably try to assert his dominance over them, thinking he's superior. He could start by showing off his powers, like his super strength and laser eyes, to intimidate the Avengers. But the Avengers, being used to dealing with powerful foes, would likely see through his bravado and not be easily cowed.