Okay, let's see...
Augustus von Langenstein went through a whole bunch of names until I realized that they were all decidedly English (Julius Augustus Morgan/Julius Morgan Augustine was a big one, though the name order changed a lot), and Gus is an 18th century Austrian nobleman. After that realization, the name just kind of happened - Augustus Friedrich Theodor von Langenstein. Really mostly just a bunch of first names I like and that happen to fit his age and location.
Jaime Peterson was originally called James Collingwood (as a Good, Solid Navy Name for the Fantasy Pirate story that character came from) until I decided she'd work better as a woman. James -> Jaime because I'm lazy, Collingwood -> Petterson, because... idk? 'S a nice last name. Might've had Pettson and Findus on my mind due to Jaime's 90's/2000's childhood or something.
Elliot de Maudeville has a slightly different story - I originally really wanted to name a character "Maude", settled on "Maude Williams", and then... accidentally created a dude, so that didn't work out. Shuffled around some syllables, ended up with "de Maudeville", and plopped a nice, short first name before it. Wilhelmina Harriet Norton was also a matter of "Hey, this first name is one I'd like to use at some point".
0813 is a series of convoluted and weird associations, but basically, "0815" is a German expression for "unremarkable and average" (it sounds better in German, I swear), but 15 -> 13 because Creepy. 14-year-old-Guardy thought this was absolutely hilarious.
Oliver the Intern is called Oliver because I like the name and always wanted to name a character that. "The Intern" is a result of me describing him as "Oliver, the intern" so much I melted my brain a little and decided that the "[Name] The [Attribute]" name construction paralleling Sonic The Hedgehog was way too funny not to stick with it.
Absalom Hayes, Lionel Cerys, Angelica Maur, Evander Halley, Dahlia, Thalerion Nevarinae, Asciadavar Dustweaver and Ettore Settimo just kinda happened, usually while drawing the character for the first time.
Severin Lapointe was the result of scrolling through Behindthename/Behindthesurname until something stuck... I think. "Severin" may have been a random brainwave, I don't quite recall. Valère Lovell was also thanks to Behindthe(sur)name, though I knew from the beginning that I wanted something with "Val" as a given name, and Aurelius "Laurel" D'Angelo, too, has his name thanks to Behindthe(sur)name... except that time I had no idea what I wanted, so I spent hours scrolling through names until something finally stuck.
For Herutaz, I knew I wanted something unusual that's also related to his general aesthetic - herutaz is a reconstructed proto-Germanic word for deer. The googling went along the lines of deer in Latin -> old English -> Old German -> googling around for words related to that -> herutaz. I originally almost went with Hircine (which is related to herutaz as a word, because language history is fun) before remembering that the Daedric Prince from Elder Scrolls exists... Also, when I said "I'm sure that German major will come in handy at some point", I sure didn't mean "I will use my language history knowledge to google for fun character names", and yet here we are.
Orephoron Sanguineus was a jerk. I started off with the Goetic demons as the obvious choice, but then decided that that was such a tired choice and I like my character names to be either unremarkably human (Gus, Jaime, Absalom, you get the idea) or actually unusual (Herutaz). Then I went to Behindthename, as per usual when I don't have a sudden brainwave while doing the art, realized that almost all "evil-sounding" names were really kind of iffy because I don't want to step on established mythology. Had Astrophel sussed out for a bit, but that name was invented for a 16th century poem. No copyright issues there, because 16th century, but it bugged me nonetheless. Then I did my usual Ancient-Language-Circuit of doom, but that didn't really bring up anything with a fitting sound AND meaning. Eventually, I took to Seventhsanctum's name generators, which also didn't work, but I eventually managed to figure out which sounds I wanted in that name, and then I Made Shit Up. And then slapped a Latin adjective on it, because why not.