Giants go back a long way. Nephelim are described in the bible as heroes of old. They are generally interpreted to be half human half angel as well as giants, but the bible is not too specific and I will leave the theological work to pastors at this point. Giants are much more powerful than humans. They have magical powers in many cultures and are almost always in conflict with the gods.
In the beginning half of the world was frozen ice and half was day. In the middle stood a cow and a giant. The cow licked the grass and up popped a god. Odin was his name-o! The giants and the gods were enemies from that point on. (I take it the cow makes a bunch more stuff, but she kind of fades out of the story.) The giants by types are: Fire Giant. Frost Giant. Vulture Headed Giant. Shapeshifter Giant. Wolf Headed Giant. Troll.
CYCLOPES, GIANTS, AND TITANS
The Greeks and Romans had regular giants, (I think they have snake feet though.) one eyed cyclopes, and titans. Not to mention freaks like Typhon. The cyclopes helped the gods during the war against the titans. You see, the Titans owned the world and the gods wanted to instead. The gods won and the cyclopes went to live on islands, the giants got put in volcanoes, and the titans were imprisoned in the underworld.
OGRES, TROLLS, AND OTHERS
Ogres are very bloodthirsty giants. They usually are very fat and ugly. A similar creature is the Japanese oni, which punishes humans in the underworld for sin. The troll can be a variety of things. That’s because when translators came across a strange creature, they often translated it troll. Trolls like those in Lord of the Rings are what I consider to be giant like. They are big and un-brainy and work for greenskins. Ettins are two headed giants, (see Ettinsmoor in Narnia and ettinmoor in lord of the Rings) and stone giants are either grey skinned or literally stone.
HALF GIANTS AND HUMANS
Although Harry Potter has trolls and giants, it also has half giants. Half giant half human. One named Hagrid is the gamekeeper at Hogwarts wizard school. Hill giants (not in Harry Potter) are just really big humans.