Amnesiac Hero: But of course. Though the "hero" part may be debatable.
Anti-Hero/Anti-Villain Between the two. He did terrible things to innocent victims for his own benefit unaware that some of his sacrifices were innocent. When he found himself murdering a young girl who couldn't possibly have deserved to die, he had a Heel Realization and resolved to atone.
And I Must Scream: His worst fear comes true should he fail in the end: trapped in the darkness he fears most forever.
Heel Realization: He finally realized he was a monster after murdering a young girl (in his words, killing an innocent to save a murderer — himself — when once he would have killed a murderer to save an innocent), and it tore him up inside. Realizing that Alexander led him down this road filled him with murderous rage, but just knowing what he had done made him wish he had died or allowed the Shadow to take him, leaving him mentally incapable of carrying out his vengeance. Wanting to stop Alexander even so...well, just look at the title for the solution he chose.
Ghost Memory: After touching the mystical orb, Daniel keeps unlocking memories that are completely alien to him, even from those who have lived and died long before he was born.
Heroic Mime: Subverted, Daniel's diary entries are all narrated by himself and the player occasionally hears him mumble and ramble to himself during game play. The subversion comes when the player first encounters Agrippa, who seems to reply to speech from Daniel, but the player hears not a peep. Possibly explained in that Agrippa seems to possess Psychic Powers, and reads Daniel's mind in lieu of conversation.
Heroic Sacrifice In the Agrippa ending he sends Agrippa through the gate to his and Alexander's world, leaving both himself and Alexander at the Shadow's mercy — and the Shadow has none. However, Agrippa is grateful and draws Daniel through to the other world after him, begging Weyer to help, and the last words of the game are his, reassuring Daniel that it will be all right.
He Who Fights Monsters: Daniel, after being mentored by Baron Alexander in how to ward off the Shadow of the Orb. The sacrifices Daniel made were criminals at first...
Baron Alexander: (While a torture victim pleads innocence and for his life) Don't pay attention to his lies! We're dealing with monsters here, after all. He set a man on fire.
Madness Mantra: Several! One within a semi-playable cutscene, "Paint the man, cut the lines!" — and the rest whenever his sanity becomes too low, which are usually denials, confusion, echoes from the past or very Lovecraftian ramblings about the progress of the Shadow.
Morality Pet: Though she never makes any actual appearance (which is probably fortunate), Daniel's chronically ill younger sister Hazel is a hint he had some redeeming features. He read books to her during her worst downturns in the hopes of helping her maintain the will to live, took the brunt of his father's rage to keep her safe, wished her goodbye before he left for Algeria, and her offscreen fate changes depending on whether the player ticks some invisible markers during the game. If Daniel is compassionate, she lived; if he's selfish, she died. His Heel Realization also hinged upon her — the little girl he murdered just before the game made him break down in regret because she reminded him of Hazel.
Non-Action Guy: He used to be an archaeologist — and not the adventurer sort. The sort that researches things in books and has to carry a parasol in the desert to ward off heatstroke. With no memory and no weapons against a collection of hideously powerful monsters and a formless abomination whose presence tears apart reality, he may as well be a bug against a windshield. All he can do is run, hide and sometimes trick threats away, never directly attack them.
Redemption Earns Life In the revenge ending, Daniel despite his former-self's transgressions is forgiven by the Shadow and practically grants him safe passage out of the castle. There are no monsters or obstacles to contend with. Brennenburg collapses only once he's reached minimum safe distance.
Sanity Slippage: It's an actual gameplay mechanic — Daniel's amnesiac mind is hanging by a thread that frays more and more with every horror he witnesses, and low enough levels see him begin hallucinating (both visually and aurally), losing control over his movements, and even outright collapsing in hysteria for several moments. But it was also the reason he drank the amnesia potion. He was physically abused as a child, and touching the Orb gave him visions which left him with "exhausting nightmares" that plagued him every time he slept. Everyone he went to for help was murdered by the Shadow (as he was guilt-stricken to learn), and knowledge of the Shadow itself focusing upon him didn't make his sleep easier. Under Alexander's tutelage, he was at first reluctant to harm a criminal even at Alexander's urging...but little by little gained more enjoyment out of the pain and death he inflicted. He devolved into a brutal sadist, but eventually hit a breaking point that brought some measure of clarity back to his mind and drank the amnesia potion to keep his crimes from tormenting him long enough to revenge himself on Alexander.
Villain Protagonist: Temporarily and only in the flashbacks. Before the game starts, he has sacrificed many people, many probably innocent, to save his own skin — although he was never told they were. It's clear once you get to the end of the story that he regrets what he has done.
Taking You with Me: After realizing that Alexander had him murdering innocents this entire time, Daniel swears to end the treacherous baron before the Shadow claims him.
The Jinx: In London, he's being constantly followed by his Doom Magnet, The Shadow, while initially its leaving him unscathed, its still killing everyone he comes into contact with. Everyone.
The Watson: In flashbacks, he's the one asking questions to which Alexander provides answers, for benefit of both his current amnesiac self and the player.
Why Is It So Dark?: After an unexplained incident when he was a child, Daniel has a crippling phobia of darkness that he retains even after his memory loss. A flashback has past Daniel being very agitated about a dark tunnel even after being allowed to light his lantern, and as player character he will breathe hard, tremble and eventually begin to whimper if made to stand in darkness for too long.
Voiced by: Sam A. Mowry
The main antagonist. Daniel gave himself the mission of murdering him, for good reason. Unfortunately, it's not as simple as he believes.
Affably Evil: It is worth noting that Alexander isn't simply evil. He's not insane, he's not sadistic, and he takes no joy in his tasks. In his notes, he expresses remorse for Daniel's corruption and the things he's done; he even seems a little shocked by Daniel's brutality.
Aristocrats Are Evil: Played mostly straight — while the Baron does evil deeds, the why of it might gain him sympathy points. As revealed in a handful of notes, he's simply trying to get back home to his family.
Never My Fault: Yes, Alexander, only Daniel deserves to be consumed by the Shadow. You didn't do a thing except make him willing to torture and kill people, telling him it was to protect himself, to get your hands on a magic orb so you can return home and receive the alchemical fuel to perform the ritual. Daniel needs to be punished, but you're innocent as the sunrise.
He researches every possible way to obtain vitae besides torturing and killing human beings, not because of any moral qualms, but because the tried-and-true method is such a time-consuming chore.
He doesn't abandon Daniel out of malice and he wasn't planning it from the start. He was even willing to take him to the other side with him. It was only after Daniel's corruption and subsequent breakdown that he locked Daniel out, fearing that he would disrupt the ritual or do something else stupid not that that stopped Daniel. However, while he regrets this turn of events, he doesn't go out of his way to incapacitate Daniel to drag him through the portal. He just leaves him behind.
Really 700 Years Old: He's existed in this world for centuries and says outright that it isn't time that ages him.
Softspoken Sadist: He's not a sadist, but he inflicts pain with meticulous care and a soothing voice.
Sufficiently Advanced Alien: One who complains at length about being forced to make do with clunky 19th Century technology using steam and water instead of the "harnessed lightning" and graceful mechanisms that exist in his own world.
Sympathy for the Hero: Despite all the ethically and morally abhorrent things Alexander has done over the years, he still feels geniune sadness and remorse in corrupting Daniel, and abandoning him to the approaching Shadow.
Torture Technician: His approach to torture is methodical and calculated, done with deliberate intent to cause maximum pain over time so he can extract more energy, and without a trace of sadistic pleasure.
Kick the Dog: He mistreats Daniel, his lackey, and subjected him to humiliation by forcing him to use a ridiculous pink parasol, arguing it would protect him from the desert's harsh sun.
Make an Example of Them: The Arabs under his employ rightfully blamed the recovered orb for all of their troubles. Knowing they might try to dispose of the relic, the Professor shot one of the men to restore order.
Psychic Powers: It's implied that whatever the gas-emitting device is that the player can choose to activate upon first encountering him allows him to read the minds of others and psychically project his voice.
Agrippa's greatest pupil, who eventually went on to become an even greater alchemist. He was able to master the power of the Orb, and used it to travel to the other world.
Ascend to a Higher Plane of Existence: Accomplished this long before the game even began. He seems to be very powerful now; making use of many Orbs without incurring the wrath of their guardians, and capable of freely transporting objects, messages, and creatures to (and possibly from) our world.
The Ghost: We never see or even hear him, but he plays a pretty big part in the Backstory. And he's present, though still unseen and unheard, in the ending where Daniel tosses Agrippa's head into the portal.
Undying Loyalty: To his mentor, Agrippa. He refused to have any dealings with Alexander until the latter freed Agrippa, and the same seems to apply to Daniel — for helping Agrippa (and at his stern insistence), Weyer is willing to help Daniel.
Bigger Bad: Though it is the catalyst for Daniel's involvement in the plot and unquestionably a thing of terror and destruction (even Alexander fears it and finds it repulsive), there are no means of communicating with it and it lacks any discernible character aside from indiscriminate wrath.
Blue and Orange Morality: There are hints that the Shadow is not actively malicious, only fulfilling its function. In the revenge ending, it decides that Alexander's death has "redeemed" Daniel and leaves him unharmed; its wrath appeased.
Eldritch Abomination: Shapeless and alien, it bends reality around itself and cannot be stopped by any normal means whatsoever. It will tear apart whatever it has to in order to reach its target and those marked by it tend to go insane before they die.
The main antagonist of the DLC of the same name. Trying to escape from her dungeon slowly reveals the details of Justine's life and how she set up her torture dungeon. She is revealed to be the Player Character at the end of the game.
Above Good and Evil: "Laws are made for cretins! The aristocracy doesn't need to know right from wrong. We are always right."
Mission Control Is Off Its Meds: Justine explains upcoming traps, puzzles, and monsters to the protagonist through left-behind phonographs, but she's clearly not trying to help the girl as much as she is rubbing her evil in the girl's face. Considering that she is the player, this takes on a very interesting light after you find this out.
Smug Snake: "Are you enjoying my quips? I think they are quite clever."
The Sociopath: It is worth noting that unlike many other examples, it is heavily implied that Justine is, in fact, a bona fide sociopath, or at least someone suffering from a severe case of Narcissistic Personality Disorder. She displays virtually every single symptom of the condition at one point or another, and her father, a psychiatrist, has been quite aware that she is suffering from some sort of mental illness (although the exact term for hers hasn't been coined yet back in the day) and experimented upon her for it.
The Voice: Until it's revealed that she's the player character.
Voiced by: Scotty Campbell
The first of the three suitors encountered in Justine. He was one of three men Justine was romantically involved with. Over time, she tortured them all and blinded one of them, and warped them into insane shells of their former selves. He was (if the sounds in his cell are to be believed) a racquet-ball player. Once a very soft-spoken person, he now attacks in the same way. He is the first man you must escape from/avoid in the trial, found in the first area of the cells.
The second of the three suitors. Basile is very different from Alois and Malo. He is angry, violent, and swears like a sailor. He is, bizarrely, the Only Sane Man of the three men, having kept one thing in mind after this ordeal — revenge — and thereby kept his mind. Possibly was a carpenter before being mutilated by Justine. He is found in the underground storage area beneath the library.
The third and final of the suitors. Malo is unique among the suitors; he is totally insane. He was a violinist before the cabinet was created. He is also much stronger than he looks; capable of tearing down doors with ease and One Hit Killing you in a flash. He is located in the flooded basement, which makes evading him difficult. He can find you even if he can't see you...though he claims he can.
There's also the fact that, if you find all the hints for his backstory, it would appear that the horrors Justine inflicted upon him simply for her own sick amusements were far from limited to simply maiming and disfiguring him. She started her work on thoroughly breaking his mind long before she even captured him: it's heavily implied that she drugged him (or at least encouraged him to drink extremely heavily) before his greatest concert yet, knowing full well that this would cause him to fumble. The great virtuoso was humiliated, mocked, booed by the audience, and eventually taken off the stage by his own orchestra mates to be replaced with some other violinist. And all the while, Justine laughed.