Of the characters listed in the “OC Adults & Historical Characters” section on my directory, everyone starting from Sir Aaron is a historical character, with most of them being the past lives of certain fankids or adults who are reincarnations. Seamus is an original Team Plasma member and Cress’s ex-boyfriend, you can just picture him looking like the generic grunt with orange hair and blue eyes.
Agnar, Dimitriy, and Jeremiah are all OCs that are related! The three of them are brothers, despite the different surnames, and are all the same kind of immortal being. In fact, they’re actually the younger brothers of Solomon (who currently is the adopted son and youngest child of Cynthia & Diantha). Their kind used to serve the deities that Arceus and Giratina were created from (that is, Ellam and Jeshir) and these four, in particular, are all the direct creations of Jeshir, making them basically his sons (and Tanith’s older siblings!)
Due to events that took place thousands of years ago when Jeshir became Giratina, they and a number of their kin lost a lot of their powers and ended up stuck in the mortal plane, though they retained their immortality. Basically, the way it works is that their bodies can be killed, but if that happens they’ll simply regenerate in the form of a child (like a phoenix), weakened, and will regain their powers as they grow, eventually ceasing to age once they’re fully grown and living on until they end up with another fatal injury and regenerate again, over and over.
Over time, the brothers all went their separate ways and all have lived many different lives over the course of history, so these are just their current identities! Agnar lives in poké!Scandinavia in a remote cabin as an outdoorsman, Dimitriy travels the world as a hitchhiker and sightseer, and Jeremiah is currently a wealthy Kalosian playboy just living it up. Solomon was a scholar until he ended up regenerating in Sinnoh after an unexpected accident (or was it an accident…) and was mistaken as an abandoned child by some hikers who found him by chance, which eventually led to his adoption by Cynthia and Diantha. He’s aware of Jeshir though and his original father being in Sinnoh is the main reason he sticks with his new family. His brothers are also aware of how their father and uncle have reverted to their original forms, as well as how they now have a new baby sister, and the three of them will play a role in Tanith, Solomon & Balthazar’s story as well as the main plot.
There’s more to this backstory, involving a fifth brother who they don’t talk about and more lore about their kind but this is getting long enough as it is so I’ll save it for a later post!