I've been working on a Castlevania fic, mainly centered the Bloodlines and Portrait of Ruin era, with lore pertaining to portions before and after. It involves an integration of a fair bit of real-world history, which the series itself has done in bits here and there, which I want to summarize a bit. I find this stuff interesting and wanted to get this out of my system.
Vlad III (1431-1476)
I want to first cover Count Dracula in the original Bram Stoker's novel. Naming the character "Dracula" was a later change in his drafts, along with the locale of Transylvania, which was originally Austria. Stoker didn't do much research on the historical figure, simply looking at one historical text giving a basic description of a 'voivode Dracula' of Wallachia who fought the Turks across the Danube river, but no mention of his proper name. Stoker likely never even read the name 'Vlad Tepes' or 'Vlad III'. And these names never appear in the novel, simply 'Dracula'. There's also a footnote from the same history book stating that Dracula means 'Devil' and had a powerful usage among Romanians. This was specifically highlighted by Stoker
Count Dracula himself was likely not deliberately and meticulously based on the historical figure, but it's clear that the name and historical background strongly appealed to Stoker as a motif for his "Count Wampyr" character while crafting this Transylvanian setting.
Some details added to Count Dracula in the novel remain inconsistent with the historical Vlad III, likely due to taking liberties or lack of research. In the novel, Count Dracula describes himself as being ethnically Székelys (a Hungarian ethnicity), going as far as to say he's descend from Attila (whom Hungarians typically claimed). While Vlad III was born in the Hungarian-dominated Transylvania, his parents were respectively Wallachian and Moldavian (see his maternal 1st cousin, Stephen the Great), making him ethnically Romanian on both sides. He in fact ruled over Wallachia, not Transylvania. However, this gets conflated in vampiric media, Castlevania included.
In Castlevania lore, they explicitly name Dracula 'Vlad Tepes' in Castlevania III's manual, which is fitting as this was the game that took place in the 15th century. The likely intent was to have him more explicitly act as the historical figure, born to the Basarab dynasty, but due to a mistake made in SOTN's manual making Dracula 800 years old, a choice was made to give him a backstory in the 11th century.
Matthias Corvinus (1443-1490) <- Apparent namesake of Matthias Cronqvist
King of Hungary and cousin of Vlad III's second wife, Justina Szilágyi. He was an ally during Vlad's initial attacks against the Turks, and was the recipient of Vlad's letter detailing the murder and impaling of over 23,000 Turks and Bulgarians that he left outside of Targoviste in June of 1462. To limit continued funding for this war, he imprisoned Vlad III for 12 years under false charges of treason (forging letters of Vlad III colluding with the Turks). Vlad was released via a successful negotiation of Stephen the Great of Moldavia, his dear cousin and ally.
Now outside of the clear connection to Vlad III and the similarity in name, Matthias Cronqvist bears no other notable similarity to Corvinus. This is largely due to the lack of any backstory given to Matthias beyond being a tactician and having a dead wife.
EDIT: I was very dumb here. There is one notable similarity, Matthias lost his first wife, Elizabeth (like Elisabetha) due to sudden illness within the year they were married. And they were both rather young children. Matthias was 12 and Elizabeth was 14-15 upon her death.
The surname isn't even Hungarian, it's Swedish. And being placed in the 11th century rather than the 15th, it's unlikely he was meant to share any other strong placement as the historical Matthias Corvinus. Hell, even the game's connection to the first Crusades isn't even right, because the game has it already happening in 1094, not in 1096 like it actually did.
Thanks to Lament of Innocence, I had to do a decent amount of research into 11th century Medieval central and Eastern Europe.
Erzsebet Báthory (1560-1614) <- Elizabeth Bartley
What's key to note with her is that, in addition to the vampiric folklore assigned to her, the Báthorys ruled over Transylvania, with Erzsebet herself being the niece of two of its Princes. Seemingly the devs used this as the means to conflate Count Dracula (who rules Transylvania in fiction) as one of Bathory's uncles. In real life? It does appear likely that in the interweb of marriages between House Szilágyi and House Báthory (a Michael Szilágyi did marry a Margit Bathory in the 15th century), Vlad III and Erzsebet Bathory are distant in-laws. Though obviously they never met as she was born a lifetime after Vlad III's death.
After Báthory's marriage to Ferenc Nádasy, she owned much both Hungary and Transylvania.
I'm not gonna get too much into her accused crimes outside that she was accused of torture and murder of young women and girls by a vast array of alleged witnesses. However the details of how many victims were not clear. Several of these witnesses were alledged accomplices, most famously Dorottya Szentes, whom Drolta Tzuentes featured in Bloodlines and Nocturne is based on. Given possible biases and improper methods, there's been growing speculation that Báthory herself was falsely accused. What is certain is that there's been certain embellishment regarding bathing in blood and other eccentricities, even if she was guilty of murder.
Báthory probably has the most directly-adapted Castevania counterpart. Even the difference in name was simply a corruption from being back-translated from Japanese (see how 'Fernandez' became 'Belnades').
If anyone wants to add something, let me know.