Vlad III, more commonly known as Vlad the Impaler. It's basically the story of Wallachia's complicated relationships with all their neighbours. The real story is so much more interesting than "spooky vampire".
Andrew Wakefield. He's the guy who published a phony study that inspired the Anti-Vax movement. More people need to learn how this always has been a scam.
I recently listened to a podcast about Antonín Švehla. Politician from first Republic (1918-1939) and master of compromise, he was as important as Masaryk but now is mostly forgotten.