The Giants are a species of large humanoid creatures that appear throughout the Harry Potter series. They are generally depicted as a barbaric, bloodthirsty species, having a penchant for violence and enjoy killing for the sake of killing.
Rubeus Hagrid, one of the series' main supporting protagonists, is a half-giant; it is known that his mother was a powerful giantess chieftain named Fridwulfa. Olampe Maxime, headmistress of the the Beauxbatons Academy in France, is also a half-giant. Hagrid's half-brother, Grawp, is a full giant, but is relatively small and does not possess the same bloodthirsty nature as the other giants.
Giants were once plentiful across the world, with at least a hundred different tribes. During the First Wizarding War, they allied with Lord Voldemort and were responsible for some of the War's worst atrocities against the Muggle community. Aurors from the Ministry of Magic targeted and killed many Giants, and forced them into hiding in remote regions of the world.
The remaining Giants retreated into a remote mountainous region in Northern Europe, and being cramped in such areas resulted in them killing each other for the most trivial matters, or sometimes for nothing but sheer violence, reducing their numbers to around eighty in total. In 1995, following the return of Lord Voldemort, Albus Dumbledore dispatched Rubeus Hagrid, accompanied by Olympe Maxime, to make an alliance with Giants and deny their forces to Lord Voldemort when Cornelius Fudge refused to make an official approach on behalf of the Ministry of Magic. The pair traveled to a tribe north-east of Minsk, to try and gain the friendship of the tribe. However, they were not alone in their efforts. Two Death Eaters, including Walden Macnair, had also arrived to try and convince the Giants to rejoin Lord Voldemort's forces.
Hagrid and Maxime were doing well, and were on good terms with Gurg Karkus. The Death Eaters, though, courted the favor of Golgomath and engineered an uprising. Golgomath killed Karkus, took his place as Gurg, and allied with the Death Eaters. Hagrid and Maxime were forced to retreat after being attacked by the Giants.
In the opening days of the Second Wizarding War, Giants were responsible for an attack on Muggles in the West Country of England, although the official explanation was that a hurricane had hit the area. The Ministry of Magic covered up the incident, but informed the Muggle Prime Minister of the true cause behind the incident.
During the Battle of Hogwarts, many Giants fought on the side of Lord Voldemort against the defenders of Hogwarts School of Witchcraft and Wizardry. They mainly battled Grawp, a small giant who had fled the colony two years earlier, and the Hippogriffs and Thestrals. It is not known what happened to them after the battle. The most likely theories are that the survivors returned to the northern colony, came to be accepted by wizard kind from Albus Dumbledore's attempt to offer them the hand of friendship, or were subsequently executed by Aurors and The Committee for Disposal of Dangerous Creatures for the part they played in the war. If it is the latter, then the race of Giants would be near extinct, with Grawp and two half-Giants remaining.