Are Diavolo and Doppio Good DID Representation?
What is DID?
Dissociative Identity Disorder, otherwise known by its former title "Multiple Personality Disorder", has a tumultuous relationship with both the public eye and popular media. There is wide disagreement as to the exact nature of the condition, with many convinced that it isn't even "real"- that it's just something people fake for attention, and only really exists in movies and television.
Indeed, DID is commonly depicted in this exaggerated, theatrical way that seems too impossible to be real. Even documentaries and books about real people said to have DID tend to be framed like horror fiction; the strange and alien "other personality", often violent and cruel, slowly but surely taking over the hapless and innocent "true self". It feels like the human mind just doesn't behave this way in reality. And it's true- it doesn't.
I think what would bring more understanding to DID in the public eye would be asserting that it is not a mystical, rare, or special condition. It is a variation of how the mind processes self-identity, an already complex and fluid mental system.
It takes a few years for a human brain to develop a coherent "self-identity" as we know it- the sense of "me vs. others", our feelings and social categories, our memories, everything about how we define "myself". This sense of self is typically managed in a way that keeps it stable and generally whole.
Trauma is known to impact these systems- dissociation, memory loss, and identity incongruence are already understood and recorded symptoms of PTSD, for example. When you sustain so much trauma that your brain becomes overwhelmed, you may go into a state of dissociation, or a detachment from "yourself" and the world around you. You may lose focus on who "you" are in these periods, your memories, your idea of where you are and how others perceive you. In other words, your sense of self becomes unstable.
DID is a complex trauma response that results when a young child, sustaining enough trauma that their brain develops around it into adulthood, forms memory and self-identity in a splintered way. Instead of forming a singular sense of self, a person with DID will detach themselves and form layers of protection from traumatic memories and feelings, manifesting with multiple different senses of self that switch out to manage trauma. These identities, commonly known as "parts" or "alters", will often have inconsistent memories (as dissociation will often cause incorrect memory formation), and they will often have separate conceptions of their names, ages, interests, and personalities, regardless of what the body has been assigned.
Identity is fluid and constantly changing by nature, and this form of fragmented identity is no different. These alters can fuse, disappear, and merge with each other over time- no two people with DID are the same. It's also common for alters to develop off of specific things, such as fictional characters or people- as it's common to take comfort in fiction and absorb personas you find particularly memorable, for people with DID, this can pop up in how their identities form. As it is a method the brain develops to manage trauma and keep the individual masked in public, it's also generally not noticeable by most people unless they know of their condition already, or know the individual with DID intimately.
Compared to many other things, Dissociative Identity Disorder is not a rare or unique condition; you could easily consider DID as nothing more than a manifestation of complex post traumatic stress. If anything, in my opinion, it's odd that we don't acknowledge DID more as a common variation of the human experience.
It's not even that far off from the fluidity of the average person's self-identity- our mental ideas of ourselves are not static, and we regularly form different senses of "self" for various situations. We have personas for our friends, for our colleagues, for our higher-ups, and more that adjust how we behave and think of ourselves. We remember different parts of ourselves, alter our behaviors, and change ourselves over time to navigate various scenarios. It isn't that surprising the brain can do this in more complex ways when it needs to.
Diavolo's Influences
The “Split Personality” is a media trope classically used in the horror genre where a character has a mind split into separate “personalities”. Traditionally, one personality will be nice and unassuming, allowing the individual to function in public- but within them hides an evil, violent “other personality” that comes out when provoked, usually to kill.
The Split Personality is not necessarily intended to be DID in every work of fiction it appears in, but it is the trope most heavily associated with it. Characters who exhibit the Split Personality trope will often be referred to in-universe as having DID/”MPD”, and when most people imagine depictions of DID in fiction, they will almost definitely imagine an example of the traditional Split Personality.
Though it's gained more criticism recently, the Split Personality still takes up the vast majority of DID representation in popular media. For decades, it dominated what people imagined DID as to the point where the general public’s knowledge of DID tended not to go beyond this trope. Sometimes, DID will even be mislabeled “Split Personality Disorder".
The Split Personality is one of many examples of media tropes that use mental illness as a horror monster. It is easy to compare, for example, to the “insane psychopathic killer” trope or “the main character was a psychotic insane asylum inmate” being a popular story plot twist. All of these depictions of mental illness gain general criticism for other-ing the mentally ill and treating them like dangers to society (when, in reality, it's most often the people with these conditions that suffer at the hands of fear, isolation, and systemic oppression).
I would also say that the Split Personality is often a lazy writer's hack for instantly "dynamic" characters with little to no effort. The trope tends to ignore the more complex aspects of DID, such as trauma, the fluidity and protective nature of alter formation, and how internal and invisible it can be to outsiders, because it simplifies the concept down to nothing more than "person with multiple personalities".
It's a depiction of mental illness that is built for performance above anything else- chances are, the two sides of the Split Personality are completely flat characters by themselves, only "dynamic" when combined. Depicting something like Dissociative Identity Disorder with care would require giving a character a complex inner world and sense of identity, and the Split Personality arises when a writer doesn't want to do that.
Mental Illness and Jojo's Bizarre Adventure
Diavolo's "Split Personality Disorder" made him the only character in Jojo's Bizarre Adventure with any canonically intended, labeled mental disorder for a very long time.
Diavolo and Doppio are an interesting case of the Split Personality perhaps just due to the nature of Jojo’s Bizarre Adventure itself. Exaggeration is a hallmark of the series; characters act in odd, sensationalized ways that people don't in real life. They tend to catch less criticism for inaccuracy than other characters like them would just because everything else in Jojo is so wild that they fly under the radar.
Additionally, while they mimic some basics of the trope (having just two personalities, one being unassuming to hide the other, etc.), Diavolo and Doppio are non-normative depictions of the Split Personality. The way Doppio collaborates with Diavolo instead of being an unwitting accomplice, for example, means they do not simply fit into the mold of "good alter, bad alter". I will delve more into how exactly they subvert their trope, but here, I just want to talk about why that is.
Jojo defies and twists tropes in general, but Diavolo's deviance from the Split Personality trope is also likely due to this depiction not entirely being based off of the fiction trope itself.
The manga mentions books and reports on real people with DID, notably including the name Billy Milligan. This individual, whose case became infamous in the late 1970s, was a serial rapist who was diagnosed with Dissociative Identity Disorder to plead an insanity defense.
If we are to assume that Diavolo's character was inspired by reports like this one, it would be unfortunate. Invoking DID to dismiss repeated cases of rape is completely nonsensical. Everything about the way Milligan's case was handled is a horrific example of the way rape has been historically defended and dismissed by the law and the public, using the mysticism surrounding DID as a shield to excuse it.
It is my opinion that this case should not be used as inspiration for DID representation at all, let alone the only named example of an individual with DID given. However, unfortunately, Diavolo is not even a unique example of DID in fiction taking after depictions like this. In fact, Milligan's case was a pop culture phenomenon for a long time, spawning plenty of thriller stories inspired by it- which makes all of this even worse to look back on. It's a welcome change that the mention of Milligan ended up being removed entirely in the anime adaptation.
I often see Diavolo being an abnormal media depiction of DID as a line of defense for his writing- I think that speaks to how many people only know to recognize the traditional Split Personality as incorrect on a surface level, not the reasons how and why it's incorrect. While Diavolo might not entirely be based off of the stereotypical DID horror trope, this isn't better- and neither do the ways he deviates from the trope in the text.
How DID Works (according to Jojo's Bizarre Adventure)
One thing that's striking with Diavolo and Doppio is the very physical way their DID is described and depicted. As souls are a tangible element of a person in the series, DID is explained as when a growing soul sustains so much "shock" in early childhood that it tears while developing and grows into two separate souls instead. DID could be pictured almost like a physical condition here- these souls are in completely severed pieces, able to function and be taken out of the body separately.
Despite this, unlike some DID depictions, Diavolo and Doppio are not referred to as two different people. They are continually referred to by the text as one individual "with different souls", which confused me on my first reading. One person absorbing or containing multiple souls is something explored throughout the series in small amounts and moreso in non-canon spinoff media such as Eyes of Heaven, but never quite like this. Diavolo and Doppio being two parts of one person is something that the manga clearly wants you to note, though.
(I'll mention that most translations of the anime adaptation seemingly change the manga's lines referring to them as one person to be vaguer or even imply that they are two people outright. Though as I don't have a grasp on what the original Japanese texts for either are saying, I can't determine what was deliberately changed and what was only a result of translation fuzz. Still, general language about the two of them seems to work off of the logic that they are one person, so I still analyze them here with that logic.)
Alongside the very physical way their condition is described, the way they switch control over the body and how Diavolo remains present while Doppio is fronting is depicted very physically. When they shift, they go through an intense, grotesque transformation where their eyes and muscles bulge and shift unnaturally. Other characters think they look so different that, until they figure out their condition, they believe them to be two different people.
Doppio displays some basic symptoms of DID, ones I imagine Araki read about- headaches, disorientation, and memory loss, mostly. (He also displays odd symptoms that are seemingly unrelated to anything about DID, like hallucinating phones, which I have always generally dismissed as a comedy stunt.) But Diavolo displays none of these. He seems to be constantly present and aware in the body, able to speak with Doppio when he needs to, watch for people who try to pry into his nature, and consciously choose to front or retract whenever he wants, though it takes him some time.
I've been using the term "DID" to describe Diavolo and Doppio's condition up to here, but it's notable that in reality, they're based less on "Dissociative Identity Disorder" than they are "Multiple Personality Disorder". I would not say Diavolo displays anything resembling "dissociating"- it's treated more like a supernatural ability he has, like he has a condition purely built to his advantage. Diavolo's main motivation is to stay hidden, and what's a better way to hide than literally retracting your own body into another?
This is the common line between Diavolo and most common depictions of DID in fiction. His DID is not built for character introspection, nor is the story very interested in exploring his trauma, identity, or anything that DID is actually about; he is not nearly a sympathetic or three-dimensional enough character to serve that role. Above anything, Diavolo and Doppio are built for story function and audience performance.
This is most easily seen with the "symptom" where Doppio hallucinates random objects as phones to talk to The Boss with. This is written purely for the sake of comedy; one background character even remarks on Doppio as a "freak" as he does this.
Is Diavolo a Demon?
All of this, among a few other factors I'll talk about, leads people to commonly theorize that Diavolo literally is a supernatural entity- that he and Doppio do not have DID at all, but they are actually displaying some kind of demonic possession. Many will go so far as to assert this as the intended textual implication.
I do not like this theory as I think whenever it pops up, it is either fundamentally misunderstanding Diavolo and Doppio's dynamic, is textually wrong or heavily anime-dependent, or is a misguided attempt to paint over the DID inaccuracy inherent to Diavolo's writing.
With only the possible exception of Diavolo's birth, there is no demonic or "possession"-like symptom they display that isn't explicitly explained by something else- their pronounced body changes and split souls are stated to be normal symptoms of DID in the Jojo's Bizarre Adventure universe. It is consistently and directly stated to be DID by both other characters and the manga's info pages. Meanwhile, there is no textual evidence or even mention of demons existing at any point throughout the series.
Devil possession is an old trope that has been associated with DID for a long time. Alongside Diavolo's obvious "devil" theming, the association being made here is obvious. However, for all intents and purposes, Diavolo and Doppio canonically have DID. It doesn't make sense to analyze them under anything except that framework. (I don't think painting over the DID for the sake of reducing ableism works either; the idea of the one and only character with DID in the entire series being a demon in disguise all along is equally ableist, if not moreso, isn't it?)
This aspect of their characters is where I run into frustrations with how the anime adaptation alters Diavolo's backstory and its narrative implications. Much of the logical foundation that creates the interpretation of Diavolo being a "possessor" only works in the context of the anime. This is something I will explain in the next section.
Which is the "Original" Personality?
(Before I get into this, understand that in terms of real Dissociative Identity Disorder, the concept of an alter being the "original" is largely nonsensical. As DID is a result of trauma from extremely early childhood, before your brain develops to where your identity can form into one cohesive whole, you develop with alters instead of ever having just "one".
For real people with DID, there is no "true form"; there is no precedent to treat one particular alter like the most "real" or "true" version of a person, as they are all parts of one whole. I must use this faulty logic for analysis purposes, but understand that it is a media-invented concept.)
Sources:
“I Am Not I”: The Neuroscience of Dissociative Identity Disorder