Two 4th wall breaking, affably evil math teachers (formerly/technically in Four's case) with humble beginnings outside of their verse (Four originating from an old educational video created by Jacknjelly and Baldi originating from the "Baldimore" comic strips mystman12 made when he was younger) who have a usually harmless-looking, albeit occasionally unnerving, exterior and nasal voices, but truly are ruthless, somewhat short-tempered psychopaths who don't have a problem killing people in, with reality-warping and LOUD AS HELL SCREAMS to boot. Both force the main character(s) to do certain tasks (amogusly susy???????), to which if they do it correctly they win a prize (somewhat in Baldi's case), and failing causes them to, as expected, get the real short-end of the stick (Four traps the losers in his own dimension which they can barely escape from and Baldi just straight up kills you), and both of their names also have to do with a physical characteristict they have (Four is literally just the number four, and "Baldi" has "bald" in it due to being Bald). Despite their unnerving demeanors, however, they are pretty comical and funny character in their own right, and only really lash out when provoked.

Ngl I can probably word or format the connections a bit better, but you get the gist.