In the Human Noble origin story, Arl Rendon Howe is notable for being the one who betrays and kills your entire family, including your young nephew and defenseless sister-in-law. When confronting him later, he mocks you about how he made your parents suffer before he killed them. He is also responsible for purging Denerim's elven alienage, resulting in the deaths of numerous elves, including an entire orphanage full of innocent children. It's also hinted that he helped Loghain sell said elves into slavery. This makes it just as satisfying to face him down as a City Elf as it is to face him as a Human Noble.
Bann Vaughan: in the City Elf origin story, he kidnaps the brides and bridesmaids of an Elf wedding and takes them back to his mansion to be raped — and this isn't the first time he's done this, either. Leliana's Song has a moment where Leliana's crew overhear him preparing to torture/rape one of his maids because of a floor stain.
In the City Elf origin, when the local priest objects that he's disrupting a wedding, Vaughan tells her that if she wants to "dress up her pets" and play with them, that's fine with him, but she shouldn't expect him to act like it's a real wedding. Yeah, it's really hard for even a Villain Protagonist PC to avoid killing him in Arl Howe's dungeon on subsequent playthroughs, even if he is a vote against Loghain in the Landsmeet.
Vaughan: Anyway, it's not like the Elves are real people.
The Awakening expansion pack gives us the Baronness, an Orlesian noble turned Pride Abomination who took her peasants' children to use in blood magic rituals. When her peasants revolted, she imprisoned them all in the Fade where she tortured them until the Warden and the Spirit of Justice came along several years later.
The Leliana's Song DLC features Harwen Raleigh, who tortures (and possibly rapes) Leliana. His men aren't that much better.
The Dwarven Paragon, Branka. As part of a long and obsessive quest to get her hands on the Anvil of the Void, she went traipsing off into the Deep Roads with several hundred members of her household following her; there, in the act that unambiguously pushes her into "irredeemable evil" territory, she willingly allows the women of her convoy to be taken by the darkspawn and turned into Broodmothers, a process that requires the woman to be repeatedly raped and violated by the darkspawn and force fed the flesh of their families. Branka didn't just allow this to happen to her friends and family (and her lover) — she engineered it in order to have a Mook Maker of her very own to test the traps around the Anvil. And when you finally meet her, she actually complains that members of her household begged for death and claims that they had no right to protest her decision. Oh, and when she learns of the plight of Orzammar? She doesn't care one bit. It's All About Me is her hat.
The PC him/herself can be one, if the player wants to do it that way. Each of the main story quests presents the PC with an unambiguously evil way to handle the proceedings: defile the Urn of Sacred Ashes, allow the Templars to wipe out the Circle of Magi, talk the werewolves into slaughtering the Dalish elves, resurrect the construction of golems, a process which you were just told in graphic detail is a truly horrific Fate Worse than Death, and take a bribe from the Tevinter magisters to let them get away with selling the Alienage elves into slavery. "The Arl of Redcliffe" takes the prize at this: you can leave the village of Redcliffe to be wiped out by The Undead, then choose between killing a child or using Blood Magic to make a Human Sacrifice to end the Demonic Possession, then (if the PC is a mage) make a Deal with the Devil to sell a young boy's soul in exchange for mystical power, wealth, or just some hot demonic sex. And that's just in the main storyline. The sidequests allow you to steal from widows, become a contract killer, break up a pair of Star-Crossed Lovers by seducing one out of their virginity and rubbing it in the other's face, and other bits of more mundane, yet still soul-crushing evil. You can be a bastard in this game.
Quentin, an insane blood mage serial killer who, in a mad attempt to revive his dead wife, horrifically murders women, hacks them up, and stitches their body parts onto a Frankenstein-esque creature. His final victim is Hawke's own mother...
Quentin is so monstrous that Orsino hiding his existence in Kirkwall just to make sure public opinion against mages doesn't get any worse almost counts as a Moral Event Horizon for Orsino.
Danarius. Quite apart from being a Magister of the Tevinter Imperium, which means he had to do some pretty despicable things to gain that position, he was the master of Fenris. Fenris fought for and won his family's freedom, so Danarius forcably engraved lyrium into his skin and knowingly removed all memories and desires that Fenris once had (which he will do again if he gets Fenris back from Hawke). When he escaped, Danarius ordered him to kill the warriors who had saved his life, knowing that he couldn't say no.
Through Party Banter, you find out that he once slaughtered a young boy at a party to show off his powers to the other Magisters.
And Word Of God has confirmed that he sexually abused Fenris as well.Dear God...
Sister ( Mother later on) Petrice was trying to get someone killed to prove how "brutal" the Qunari were, to purge them from the city. She also had her men murder Viscount's son Seamus inside the chantry because he was a convert to the Qun, and so she could blame Hawke, a supposed Qunari supporter.
Her bodyguard, Ser Varnell, also counts. He outright kidnaps a bunch of Qunari and tortures (later murders) them in front of an Angry Mob.
Sers Alrik and Mettin of the Templars are everything Anders hates about the Order:
Alrik is a sadistic bastard who abuses the Rite of Tranquility by illegally Tranquilizing mages who passed their Harrowing, threatens more reasonable Templars who protest his deeds, and drafts a plan to make all mages in Thedas Tranquil. When you see him in "Dissent", it's heavily implied that he uses the Rite of Tranquility to make pretty mages into willing sex slaves.
Mettin is willing to kill not only apostates, but the friends and families who protect them as well. He even turns on his more reasonable partner, Ser Agatha, when she objects to his slaughter of innocents.
If Hawke supports the mages at the beginning of Act III, you'll eventually walk in on Mettin and his men about to kill a woman in Lowtown. Her crime? Offering her mage cousin a place to stay for the night while she was fleeing the Circle. And as soon as Hawke and co. walk in, he immediately orders his men to kill them to eliminate any potential witnesses. If the player had any doubts that the templars were Putting on the Reich in the third act, Mettin eliminated them.
