My go-to humanoid is hobgoblins; Lew Pulsihper calls them 'Rick's Nazis'.
But the scary monster in my 1e game is - the bugbear.
The word 'bugbear' is from the 16th Century and means, at heart, 'big, hairy monster that eats children'. A literal meaning of 'bugbear' is close to 'supernatural, man-eating creature covered in fur'.
The description in the AD&D Monster Manual should be chilling; bugbears are within a hair as tough as a black bear or wild boar, have a good armor class, and are strong. Strong enough to open combat by hurling footman's maces 4"! Plus, they are stealthy and surprise foes half the time. And their description? 'Giant, fur-covered goblins with a shambling gait'.
I picture (and describe) their movement as being similar to this:
Odd, unnatural, uncanny valley monster movements.
Bugbears also see very well in the dark. For players in my campaigns their first encounter with a bugbear is sometimes like this;
The people of Seaward, especially the peasants, are terrified of bugbears because of their stealth and hunger. Bugbears are known to snatch children out of their beds at night without parents or dogs knowing until it is far too late. The villages in the rill valley sometimes call the Briars the Bugbear Woods to ensure their children stay away.
What monster do you use to scare players?