Amnesiac Hero: In keeping with the series' Meaningful Name. The main character, Oswald Mandus, cannot remember the last few months of his life, and is driven to rediscover what happened to him, what went on during his trip to Mexico, and how he is connected to the Industrialized Evil around him.
Anti-Hero: Mandus killed his sons, sent orphans to clean pipes that'll burn them alive if they stick around too long, fed the surviving orphan cleaners to the pigs, created a Mad God from his soul who murdered thousands, and performed horrifying experiments on humans and animals. After he gets an amnesia, though, he regrets everything he did and sets out to fight the real villain, The Engineer.
The Atoner: To an even greater extant than Daniel, from the previous game.
Badass: Out of all the Amnesia protagonists, he is without doubt the bravest. Considering his willingness to dive into what is essentially a mechanical hell without rancour or hesitation in order to save his children, and then his red-hot fury when he realizes what the Engineer has caused him to do. How many other protagonists from this series have told off an Eldritch Abomination? In addition, he is perhaps the only one capable of actually some destroying the monsters that assail him; the Tesla Pigs explode if he flickers his lantern at them.
Badass Beard: According to the Frictional Games, this picture◊ of a Victorian gentleman is an approximation of what Mandus looks like. Combined with Mandus' extreme Papa Wolf tendencies and sheer determination, he is indeed quite badass.
Badass Boast: When endeavoring to destroy the Engineer, he refers to himself as an 'Angel of Vengeance'. And then there's this:
I have you now, creature. I will destroy you.
Determinator: To an almost comical extent, initially born out of his fierce love for his sons, and then by a sense of personal responsibility.
Gadgeteer Genius: Implied as part of his success as an industrialist. Even the recording and playback devices, though not an original concept, are his own design.
Go Mad from the Revelation: Mandus seeing the future drove him nuts enough to murder thousands to try and stop it, including his own children.
Humans Are Bastards: His rants are often littered with misanthropy, and he has utter contempt both for the "filthy and brainless" lower class and the rich and "enlightened" upper class who happily allow the suffering of those "beneath" them to continue. However it was his visions of the far more horrifying atrocities humans would commit in the 20th century all over the world that caused him to snap and create a machine to "make pigs of them all"
Hypocrite: He holds vehement disdain over the industrialization of the 20th century, yet he practices in Industrialized Evil himself. In fairness to him, there are some hints to imply he may have been mostly manipulated by the Engineer to doing so.
Love Makes You Evil: Mandus murdered his own children to spare them an even more grisly death at the Battle of Somme years later.
Meaningful Name: Oswald Mandus is a play on Ozymandias, referencing his obsession with making his factory the "great work of the industrial age".
Offing the Offspring: After seeing his children would die horrifically in the war, Mandus cut out their hearts as a ritual sacrifice in hopes of creating a god who could save the world from the slaughters of the 20th century.
Papa Wolf: Despite being scared out of his wits and hunted by an army of nightmarish Human/Pig abominations he still willingly dives headfirst into the madness and terror of the machine in order to save his children. He is fiercely devoted to them as well, as evident in one journal entry where he outright states he would die and kill for them. However, this trope is also tragically deconstructed as he killed his sons before the game started in order to save them them from dying far more horrible deaths in World War I. The revelation of doing so drives him to the brink.
"I want my children, you UNHOLY BASTARD!!!"
Redemption Equals Death: To protect all of London from becoming sacrifices to the Engineer, Mandus re-merges with his creation, killing them both.
Tranquil Fury: When he finds out what happened to the children in the tubes, he stops talking, focusing only in killing the Engineer (and ultimately, himself).
Walking Spoiler: Considering this guy is the protagonist.... that is quite the achievement.
Well-Intentioned Extremist: Initially, flashbacks of what appear to be earlier stages of his "collaborations" with the Engineer show Mandus as being uncomfortable with the monstrous actions he eventually convinces him to undertake. Later on, he seems to truly believe what he was doing was truly necessary and ultimately positive. And yet, when he beholds the Machine's motives in full for the first time...
Oswald Mandus: (near weeping) Oh God, oh no. What have I done? No! This is not what I meant! This is not what I meant at all!
Voiced by: Mark Roper
A God Am I: Due to the Orb's power and the countless sacrificed to it, as well as his "mission" to prevent the horrors of the 20th century it considers itself a god.
Deus Est Machina: The constant sacrifices are meant to turn it and the piece of Mandus' soul it contains into a bloody god.
Eldritch Location: due to the abruptly shifting, warping, and maddening nature and layout of the machine it qualifies as the latter, which coupled with it's unfathomable power qualify it as the former.
Omnicidal Maniac: Has twisted countless people into the tortured manpigs and plans to use them to slaughter the entirety of humanity by feeding them to the machine.
Also his quotes about "splitting the egg and the atom" heavily hint that his plans are to annihilate the entire planet with the power gained from the slaughter of London's population. This is basically confirmed by cut dialogue in the game files
Psychotic Manchild: For all its' crimes and follies, the Engineer is almost like a bitter child happy to wish away all the problems of the world and humanity. Right up to begging "Daddy" Mandus to not kill it at the start of the game.
Offing the Offspring: Both were killed by Oswald to prevent them from dying horrible deaths in World War I.
Walking Spoiler: Not quite to the degree of the above, but certainly not nonexistant!
Lillibeth "Lily" Mandus
Oswald's wife, whom he seemed to have loved very much. She apparently died giving birth to Enoch and Edwin. The only time when she is mentioned is through Oswald's journal entries, which are received through the course of the whole game.
Psychopathic Manchild: Can sometimes be seen playing with children's toys. They are also violent psychopathic murderers.
Suspiciously Similar Substitute: From the torso down, it looks a lot like a Servant Grunt from the last game. Which makes sense since Mandus was able to acquire the corpse of one and use it as a study.
Teleport Spam: near the ending of the game, you find Manpigs that are particularly affected by the Compound X, resulting in their bodies emitting an electrical charge and flickering in and out of existence. Luckily, light makes them explode.