Eldritch Giants are a lesser giant strain in the various worlds of Dungeons & Dragons. They debuted in the Monster Manual 3 for Dungeons & Dragons 3rd Edition. Here, they were presented as the diminished remnants of a giant strain which developed a powerful affinity for manipulating arcane magic, only to then lose all but a relative fragment of their former might. Now they dwell in isolated mountaintop fortresses or in deep caves near wellsprings of magical energy, largely seeking to hide from the world and focus on studying in order to unlock their lost ancestral might. They have a particular enmity for Storm Giants, for reasons never really clarified, but they are generally more interested in studying magic and training as wizards or similar spellcasting classes to go and pick fights.
They later returned in the Monster Manual 2 for Dungeons & Dragons 4th Edition. Here, they were presented as a giant strain whose inherent connection to arcane magic had caused them to migrated enmasse to the Feywild, or perhaps to have even sprung into existence in that plane of existence.
In both editions, Eldritch Giants can be distinguished by their purple skin and love of weird tattoos of magical sigils and designs.