Who doesn't love a good giant? The Norse certainly do.
Meet the Jötunn (pronounced yo-tunn) (plural is jötnar). Often called, in English, the Frost Giants. They're a race in the Norse mythological world. They live in one of the nine Norse worlds, Jötunheimr. They were banished there by the Norse gods, the Aesir, who didn't want them hanging out in Asgard.
Also, I should say from the beginning that they aren't necessarily giants as we think of giants in English. A more accurate translation from the Old Norse calls them devourers. If you ask me, that's a lot scarier than a plain old giant.
What do they look like? Complicated. Sometimes they're humanoid, sometimes they're not (remember 2 out of 3 of Loki's kids?). Sometimes they have one head, sometimes they have more than one. One guy even had nine (in case you've noticed, the Norse LOVE the number 9). Sometimes they're described as hideous (claws, fangs, and deformed features, apart from a generally hideous size), sometimes they're beautiful (beautiful enough that some stories revolve around the Aesir forcing non-consensual relations with them). Basically, as with much of the Norse mythology, there's a lot of conflicting accounts.
Some of the Jötunn are even fire giants, instead of frost giants. So there's a lot of variety in the Jötunn, just like any other race. Norse mythology is actually incredibly well developed. Lots of diversity among all of their races, not just the humans. But, back to the fire giants. In Ragnarok, it's their job to set fire to the world and burn it to the ground. Pleasant.
So let's talk about why they're scary. They're beings of chaos, destruction, and decay. Basically, they are trying to drag the world back to primordial chaos. The Aesir are trying to civilize the world (sometimes) and see the Jötunn as a threat to that.
Mind you, they aren't always the bad guys. They often interact with the Aesir and the Vanir (the two factions of Norse gods) and not always in terrible, horrible ways. Let's just say it's a complex relationship. Sometimes they even intermarry. Some have babies. Remember Loki's darling babies from last post? Yep, all of them call a Jötunn mommy dearest. Not only that, but most of the gods are descended from the Jötunn. Odin is half Jötunn, and Thor is 3/4 Jötunn.
I'm mostly only including the Jötunn in this monster mash because of the way popular culture. Although they get much more complicated backgrounds in Norse mythology, pop culture general tends to villify them, making them terrifying monsters. See the first Thor movie, for instance. But despite us calling them giants, they aren't necessarily the bad guys.
So that's the Jötunn. Giants. Complicated giants.