People with at least four PhDs This is a question of pure curiosity: just like there exists polyglots who speak dozens of languages, are there any cases of people obtaining at least four PhDs? (It is okay if topics are fairly close, e.g. Maths, stats, cs, theor phys).
Note, I am specifically not asking about whether doing multiple PhDs is advisible.
In German-speaking countries, or at least in Austria, the abbreviation DDr. mult. is used to denote people who have more than two doctorates. Googling for DDr. mult. allows one to identify some persons, but I cannot quickly verify whether they received just three or even four+ such titles.
However, note that some of them should actually be labelled DDr. h.c. mult., whereby h.c. (honoris causa) suggests that the doctorates are honorary titles. In other words, oftentimes they did not start PhD programs from the beginning to the final defense of their dissertation multiple times, but perhaps just once, whereafter they received some honorary titles for some public service.