fluorine chemistry is full of extremes, because the intense greediness of fluorine for attracting electron density (i.e. its "electronegativity") gives rise to some unusual chemical contrasts. F is tends not to behave quite like Cl, Br, or I, its periodical relatives.
the other halogens have long been known to form "halonium ions", hypervalent cations in which the halogen bears two or more organic substituents and a formal positive charge. R2Cl+ (chloronium), R2Br+ (bromonium), and R2I+ (iodonium) ions were known since 1970, having been verified by a minor god of organic chemistry, George Olah, working in the "magic acid" SbF5 solutions that furnished Olah with so many great discoveries. many iodonium salts are important reagents.
but fluoronium ions? why could the world's most electronegative element ever be persuaded to bear a formal positive charge? well, these folks (some of them) were willing to spend twenty-seven years finding out, and that's surely some sort of martyrdom. the paper is remarkably detailed and entertaining by the standards of contemporary chemical publication (DOI: 10.1021/acs.accounts.9b00554), and you get a nice picture of some of the blind alleys they went up on their way to a stable fluoronium ion. they succeeded, although molecular-orbital calculations indicate that most of the positive charge is actually distributed among neighboring atoms while the F is still partly negative. an oddity indeed, and someone(s) spent a good fraction of their life making it.