D&D Monsters: Hill and Stone Giants

Giants are a recurring figure in myth and folklore, appearing in the stories of just about every real-world culture. There's something fundamental about the idea of people who look vaguely like us but are much larger and stronger. There is, of course, considerable variation among cultures as to what giants are supposed to be like, and even D&D reflects this by having six different core types, even before we get into one-mention specials or other creatures that are, in some sense, gigantic humanoids (such as ogres).

As is common where variants of the same idea for a monster exist in 1E, the six basic giants are arranged in a clear hierarchy of power, with each type having one extra hit dice, one extra point of strength, and delivering one extra die of damage than the one below it. Unlike some other creatures, while the details change, this progression of power remains the same in later editions. 

D&D Monsters: Bulettes

The bulette is a creature original to D&D. Like the owlbear, it's based on a plastic toy from Hong Kong, in its case probably meant to represent some sort of kaiju, although it's hard to know for sure. It's one of a minority of original monsters to have an actual name right from the start, rather than a descriptive term ('mind flayer', 'carrion crawler', 'trapper'). 

Incidentally, Gygax originally intended the word to be pronounced as "boo-lay", and official material from WoTC, and TSR before them, used to insist on this - and maybe still does. This raises a question, often seen in fantasy literature more generally, of "then why didn't you spell it that way?" In this case, I'll note that both the spelling and the supposed pronunciation appear vaguely French, which may be intentional - although, obviously, they don't match up with one another in that language either...