You probably haven't heard of Empedocles, but I can guarantee you've heard of his most famous theory.
Empedocles was the guy who came up with the idea that everything is made from earth, air, fire and water. The four classical elements.
It's sort of ironic that Empedocles lived at the same time as the guy who first realized everything was made of tiny little particles. The two theories competed for centuries, and in fact the particle theory had the edge well into Roman times. It was after the fall of the Roman Empire that Christian monks decided the particle idea was obviously rubbish and went with the much more sensible earth/air/fire/water system, thus dooming western civilisation to a few extra centuries of chemical ignorance.
The four elements remain popular to this day in astrology and alchemy and fantasy stories. Not to mention modern music. The band Earth, Wind and Fire is named for them.
Empedocles was into distinctive clothing. He walked about wearing a purple robe and wore sandals made of bronze. That must have been incredibly uncomfortable, but these sacrifices must be made if one is to be the special anointed of the Gods, which Empedocles firmly believed himself to be. I'm afraid it was the sandals that contributed to his greatest debacle.
You see, Empedocles considered his genius to be so great that he deserved to spend the rest of eternity in the company of the Gods on Mt Olympus.
The tricky point was to convince people that this had actually occurred, after he died. Being Empedocles, he came up with a brilliant scheme. One night, in his old age, he crept away from his friends -- so that they'd think he'd mysteriously disappeared -- and threw himself into the nearby volcano, Mt Etna.
This crafty plan went horribly wrong a few days later when the volcano had a minor eruption. One of the bronze sandals was disgorged. His friends found it on the slope and had no trouble guessing where Empedocles had gone. I confess I'm somewhat reminded of the grand schemes of Wile E. Coyote.
Empedocles is about thirty years old when Nico and Diotima begin their career as investigators. Yes, this means that at some point, Nico and Diotima (and Socrates) are going to meet him.