An underrated character who stands out to me never appears on page. The Smeltings school nurse who finally makes Petunia realize that her son is morbidly obese.

The most underrated character is Dennis Creevy, Colin's younger brother. He snuck out to Hogsmeade and joined Dumbledore's Army in his SECOND YEAR. In his first year, he swam in the lake with the giant squid. He was fearless!

The idea of Madam Hooch showing up in the Battle of Hogwarts and flying around fighting from the sky, might be my favorite takeaway from this entire video.

That whole bit about Justin, Zacharias and Ernie was brilliant. I didn’t think there were people who obsess over details like that, I’m glad to be proved wrong

While still a fairly well-known character, Madam Pomfrey is arguably the most underrated in the series. Her healing abilities are exceptional in a world where there are endless possibilities of terrible injuries, and Harry ends up in the hospital wing multiple times every year he's at Hogwarts. We almost take for granted how much she comes in clutch in the series.

That thing about Madam Pince shows how little JKR knows about librarians.

I do imagine Gideon and Fabian Prewett swelling with pride from beyond the grave when Molly drops Bellatrix.

Crookshanks. Final answer

4 characters that I thought about:

Amelia Bones: Gave Harry a fair trial when the room was filled with people who wanted him convicted, especially Fudge and Umbridge.

Greyback: Interesting and one of the most memorable villains, however stands out since he was different goals compared to Voldemort. It's an interesting thought experiment what would happen to him and his movement if Voldemort won. Because Voldemort doesn't seem to think highly of werewolfves and we know what happens to those Voldemort look down on.

Bob Ogden: I had forgotten his name but I love his memory, it's rare that we get to follow a minor character this closely but it's a great chapter and he's a great character imo. If you have forgotten, he visits the Gaunts.

Firenze: Great character who makes us understand a whole other world.

I think Hedwig is the most underrated character.
She is the only steadfast friend of Harry’s through out the series.
She brings him comfort, information and companionship.
She is also his only contact to the wizard world.
They had to make her quiet and unsociable at the end to soften the blow of her death. Which was extremely tragic in the way it was handled in the book.
The movie writers at least saw this and made her a heroine in coming to save him.
I thought she deserved a much better ending and she was technically the first to die in the Deathly Hollows.

I think a very underrated character is Rufus Scrimgeour. If you think about it, he took on a job destined to fail with Voldemort already infiltrating the ministry and most of his inferiors either under the Imperius curse or a blood supremacist. He went to Harry to try and join forces because who else was he meant to form an “alliance” with. His last ever action was to protect Harry in the best way he could to deny Voldemort. He reminds me of Churchill as a flawed man trying his best to defeat a vastly worse enemy

I really hate ludo bagman and winky wasn’t in the movies. They were sooooo important.

Madame Hooch is actually a pretty bad teacher and referee. In the games she referees all sorts of things happen to Harry, and she does absolutely nothing about them.
His broom is jinxed by Quirrel, a bludger controlled by Dobby torments him for a whole game and breaks his arm, a freaking army of 100 dementors invades the pitch and knocks him unconcious, and yet Madame Hooch barely seems to notice what's going on. It's always one of the teachers or Harry's friends who have to intervene and save the situation.

The portraits are underrated, since people assume they're just guards you can talk to when in reality they're sentient beings, doomed to be trapped inside a picture frame for all eternity.

Florean Fortescue, the true hero of the story

I think Draco is best read as Lawful Neutral. He’s not impulsive… he usually works through systems and authority. He respects the Ministry, joins the Inquisitorial Squad, and constantly tries to get Harry in trouble in front of teachers instead of acting outside the rules.

Yes, he repeats the pure-blood ideology he gets from Lucius, so a lot of his dialogue sounds evil. But his actions tell a different story. He wishes Hermione dead in one breath, yet privately acknowledges her talent and is struck by her at the Yule Ball. That disconnect between what he says and what he does is key to understanding him.

His worst act is probably the Katie Bell incident, but the text implies remorse. He talks for years about hating Dumbledore, yet when he finally has the chance, he can’t kill him. He refuses to identify Harry at Malfoy Manor. In the Room of Requirement, he just wants his wand back and is horrified when Crabbe escalates things.

He echoes his Lawful Evil father, but when push comes to shove, he doesn’t follow through. The books don’t give him a full redemption, but by the end it feels like Draco is no longer invested in pure-blood ideology and wouldn’t back another movement built on it, even a lawful one.

I think it's bit unfair to say that Ernie is obsessed with his lineage. He talks about it once and only to protect himself from suspected heir of Slytherin.

Colin Creevey is very underrated and deserved to live. That death broke my heart

Harry even says it himself. He didn’t feel like a wizard until he flew on a broomstick

I always assumed all these years watching the movies that Harry didn't even like quidditch all that much.  Currently reading the books for the first time, I love how almost obsessed he is with it in the books and how it really is a major part of his character