NE555 is not "unknown" (most popular chip in the entire history of electronic engineering), 74xx and TL072 are not unknown either, anyone who knows a little bit

NE555 is not "unknown" (most popular chip in the entire history of electronic engineering), 74xx and TL072 are not unknown either, anyone who knows a little bit of hardware knows the chip. TL431 is popular yet unknown to most people outside the world of switched-mode power supply. I think the OP wants some popular yet relatively less-known chip to those who is outside of the field.