Board Thread:Anime/Game Discussion/@comment-8851503-20190414110237/@comment-26540901-20200120010726

RevineYT0 wrote: I think that Diavolo was the original personality and then he developed Doppio so  that he can continue his crime and act like a non-suspicious person while doing so, and the reason why I think this is why is because Doppio is very kind so if Doppio developed Diavolo, then 1. Why would Doppio be taking actions for his younger personality (because who knows if Diavolo can wipe his memory) and  2. Then he wouldn't be the kind person that he was, he would just be a mean person. Also, I think that Diavolo was the original personality because according to the wiki's Doppio article, it says that Doppio is the younger personality, so if Doppio is younger then Diavolo, then either when Diavolo takes control, Doppio doesn't age, or Diavolo is the original personality. I rest my case.

shows signs of DID (Dissociative Identity Disorder) and Schizophrenia, such as Memory Loss/Amnesia, Headaches, Hallucinations (Mostly phones) and Unawareness that he and Diavolo share the same body. The Theory behind DID is that the mind as a defense/coping mechanism switches to a different personality resulting in a blackout for the main personality. So a person with DID tends to switch personalities when they're extremely angry or pressured into uncomfortable situations. This is seen several times with Doppio, as every time he was pressured/harassed, he switched to Diavolo/Diavolo took over, with Doppio having no idea what happend during that time and having a headache afterwards. While Doppio is a polite man, he can be quick to anger and act bipolar once stressed.

The boy seen in the flashback had fashioned his hair into a braid like Doppio and Doppio fits the "honest but dim" description better. In the extended flashback in the anime, the baby also had Doppio's eye color and the boy had freckles, like Doppio. Doppio's voice actor, Soma Saito, also voiced the boy in the flashback, implying it even more. When Silver Chariot Requiem swapped everyone's souls, Diavolo wasn't transferred to a separate body, but instead his soul latched onto Mista's body which had already another soul in it, implying that Diavolo needs a Host to be able to live on while Doppio was transferred to Buccellati's body where he was able to live on alone until he was killed by Mista. When Polnareff explained DID, he used Billy Milligan as example who had a split personality which was muscled like a boxer (When Diavolo took over Doppio for the first time on screen, Doppio's body became buff). When the Mangaka of JoJo drew all the Main Villains in one picture, it was Doppio there, not Diavolo. The episode in which Doppio appears for the first time together with the backstory is called "A Little Story From The Past my Name Is Doppio" (Manga) while Diavolo's first full appearance is in the episode called "His name is Diavolo" (Manga). Doppio also has a full name, with the only Antagonists in the same part who have one as well being Mario Zucchero and Risotto Nero, while Diavolo doesn't have one. It was also confirmed in a Q&A that all added or extended flashbacks in the anime are canon, therefore making it highly likely for Doppio to have been the original personality until Diavolo became the dominant one.

A split personality is basically created from trauma, to protect the original one. Doppio is fragile, Diavolo is strong. Doppio is unaware that Diavolo is in him, while Diavolo is aware that he's in Doppio and uses him, the split personality is always aware while the one who has the split personality is unaware.