Capcom is known for taking religious figures/mythological beings and everything and anything to do with heaven and hell and implementing it into the games. I mean I don't think these people have ANY limit to their creativeness. It boggles my mind if I really try to sit down and dissect every little thing they've put in, because you can trace the origins of the craft if you focus on it - but I have the attention span of a fly. I always assumed Capcom was secretly in league with the creators of the Gintama anime, because let's face it, Gintama has everything and everything in every episode, and sometimes they're blunt about where they got their material from. Gintoki could have been a Vergil and Dante crossbreed. They've even got a friggin fangirl in the actual anime who goes all-out fangirl on Gintoki. It's like the anime version of Scary Movie - they rip off all the other animes out there. Point is, DMC x Gintama, they snatch a lot of already existing characters and concepts and just tweak them a bit so no one can scream copyright infringement.
Off topic, I'm sorry!!!!
Okay, so, point I was actually getting at is, we know where Vergil and Dante's characters stem from. I mean, Dante's Inferno, says it all. We also know where Sparda's character stems from, eg. Mundus=God, Sparda=Lucifer, with Sparda being Mundus's most beloved and highest ranking servant, Sparda rebelling against Mundus, then throwing himself willingly from the demon realm into the human world where he lives as a 'human' trying to keep the world in harmony, eg. Sparda becomes the demonic version of Jesus. So, we've got those major character's inspirations pinned down.
Where the heck did Nero come from? It's got to be something big, like right under our noses right? It's something everybody has heard of at one stage or another. Maybe they've taken him from historical events? I still haven't pinpointed down where Nero came from
Maybe Ceasar Nero? But I doubt he was a warm blooded, passionate type, so that would make no sense.