Titus Andronicus is deemed the first attempt at a tragedy by Shakespeare, written in 1594, however it is notable especially in its distinctly gruesome style. While the outset presents a story of an endless revenge cycle between Titus, the jaded Roman general, and Tamora, the new empress whose son was slain by Titus in an act of sacrifice in all too recent past, and Tamora is presented as the clear villain in the very beginning, Aaron the Moor, a humble moor-turned-slave-turned-Tamora's-lover emerges as the orchestrator of most, if not all the true horror the play puts on show. He is as the play describes, "chief architect and plotter of these woes", and his actions go far beyond what one would consider PE.
Aaron is one of the earliest written psychopaths in literature. His entire goal is to spread misery and mayhem, to ruin Rome, and he claims his soul will be "black like his face". This leads to a theory some scholars have entertained, that Aaron might be a victim of racism which was prevalent of the time, but the monster merely appears to embrace this, boasting that since he is black, no one can see him blush, and so he can exploit everyone's emotions under a seemingly honest facade. The moment Tamora becomes empress, Aaron sees a path paved through which he can wreak havoc on a much larger scale that he is wont, though his past we will get into a bit further down.
The other villains and heroes alike in the story commit crimes such as murder or the planning thereof wholly in acts of vengeance (an odd-one-out example being Titus who has Tamora's son executed in what he believes is an honorable sacrifice), but Aaron quite honestly only performs his evil deeds for his own sick satisfaction, perhaps embodying the for others subconscious sadism every shift of apparent noble revenge is lathed with. Aaron brings to pass the most prominent conflicts of terror in the play, namely:
Convincing his two peers to kill the husband of Titus' daughter Lavinia before raping her, cutting our her tongue and chopping off her hands so she will live in agony without being able to tell others of the perpetrators (a horrific measure Aaron later smugly refers to as "trimming" her), then framing Titus' two sons. He goes to the father and falsely claims that if he cuts off his one hand, they will be spared. In understandable despair, Titus obliges, however when he thinks he is sent back his sons, he is instead greeted with the sight of his own severed hand betwixt his sons heads. Aaron watches this through a crevice in the wall and cracks up into a hysterical laughter seeing Titus go mad with grief.
Aaron then, being Tamora's secret lover though she is of course married to the current emperor Saturnius, finds that she has given birth to his son, who is naturally black, which would give away their affair. Aaron stabs the nurse that brought the baby hither to death, then concocting a plan to kidnap a random white baby and pretend it is Tamora's, so that he may not be found out. He runs off with the baby (we will get to this later), but is caught by Lucius, the only surviving son of Titus and the upcoming emperor, and confesses gleefully to his crimes, revealing that he regrets only that he had not done a thousand/ten thousand more, and repenting only any good deeds he might have done in life. He is so horrible, that Lucius, who has been witness to all the other violence in the play, doesn't even worth him the hasty death of hanging, but instead buries him in sand with only his waist and up emerging from the ground in the desert, to famish him.
Indeed, with all this, Aaron can be described as the Satan of the play, the incarnation of Vice and the genesis of all the calamity.
MORAL EVENT HORIZON
He obliterates the Moral Event Horizon per the deeds detailed above, and as the final nail in the coffin, he avows repeatedly in the end that he rues nothing, and merely hoped he could've caused more torment.
It all comes down to his power. He reveals well near the end that before the events of the story, he would perform cheaper acts of Pure Evil:
"Even now I curse the day–and yet, I think, few come within the compass of my curse,– wherein I did not some notorious ill, as kill a man, or else devise his death, ravish a maid, or plot the way to do it, accuse some innocent and forswear myself, set deadly enmity between two friends, make poor men’s cattle break their necks; set fire on barns and hay-stacks in the night, and bid the owners quench them with their tears. Oft have I digg’d up dead men from their graves, and set them upright at their dear friends’ doors, even when their sorrows almost were forgot; and on their skins, as on the bark of trees, have with my knife carved in Roman letters, ‘Let not your sorrow die, though I am dead.’"
However, in the play his first true soliloquy is when he rejoices at Tamora's new title as empress, discerning that he will now have the might to destroy Rome, as he has her as his secret mistress.
He has a terrifying moral agency, and savours the mental and physical trauma he can impose upon others. When describing how he watched Titus lament the loss of his two sons, he says outright:
"When, for his hands, he had his two son's heads; (I) beheld his tears, and laugh'd so heartily, that both mine eyes were rainy like to his!"
This goes to show that he is perfectly aware of the Hell he had put Titus through, and that he had thought it was the funniest thing.
He also says he wishes he were a Devil, understanding he is nigh the incarnation of evil.
NO REDEEMING QUALITIES
A lot of scholars and those who dredge for sympathy in villains like to point out the fact that Aaron is hellbent to save his baby son in the final two acts of the play. While this is true, his dialogue implies not necessarily anything close to a wholesome, fatherly love. He calls Tamora the "devil's dam"; alluding to his son being a demonic creature, says his child will be above all else for since he is black, he cannot blush, and that he is to be trained in a cave to become a warrior, indicating that he sees him as just another vessel of pure evil and sadistic manipulation (solidified as he calls him "me"), and finally refers to his very own baby son as a "thick-lipped slave".
In this very scene, he slays the Nurse, and the aforementioned readers like to conflate the nurse's pleas that they should kill the baby for the safety of Tamora and her admittedly ruthless racist commentary. But if one reads the scene, one can see that while Aaron is indeed enraged by her commentary, he kills her not before inquiring about those bearing witness to the birth, showing that he just killed her to tie up any loose ends that might unravel his secret affair to the masses. Immediately posterior to disemboweling this woman, he makes a joke about her final cries sounding akin to a pig ready for the spit.
Ultimately, his obsession with his son is more of a mystifying notion of an evil legacy than a sudden pang of innocent love -- this can be compared to Captain Vidal from Pan's Labyrinth who, in like manner, is much too irredeemable to be ruled a potentially caring parent.
Yeah no, other than the stretch of somehow relating this to the intense racism of the time, which he embraces rather than shows some sort of Tragic Reaction to, there's really no way to excuse, or even so much as understand Aaron's fiendish disposition. He doesn't want you to understand either, as he in his final moments nought but blusters about his evil.
Yes, the murder of the nurse, the planned murder of Lavinia's husband and the rape and mutilation of the girl and the severed hand and two heads of Titus and his sons respectively are all visually presented as the plot unfolds.
All his earlier crimes (murders, devised murders, rapes, arson, digging up dead bodies and haunting the loved ones of them) are but an off-screen cherry on top.
He is the worst.
In the end of the story, he is described as:
"That damn'd Moor, by whom our heavy haps had their beginning".
Underscoring that he is the root of all the worst and most brutal aspects of the iconically brutal play.
And the play is iconically brutal, though stabbing and killing is no stranger to Shakespeare. In fact, to name an example, Iago from Othello, another Shakespeare PE, plans mere murders, but it is he who is the engine of tragedy in the play. Aaron, rising above the mere murders in this tragedy, provides the audience with what has stuck as the most harrowing story beats of all: The relentless rape and mutilation of a daughter, the bloody decapitation of sons (even though the father lopped off his own hand to save them), the casual killing of a terror-stricken nurse, never mind all the crimes committed well before the curtains even rose; and what sets Aaron apart and truly wrings out the travesty of his actions is that unlike every other character in the play, he had no genuine motivation, but only the rotten desires of his heart.