Ogres are rapacious, bestial giants. They are closely related to trolls, and are distantly related to the various races of giants. The "runts" of the giant litter, they possess little more than feral instincts and brute strength, and they revel in the abuse of things smaller then themselves like cruel children.
Ogres are quite materialistic, and are apt to work as mercenaries for treasure -- especially anything shiny.
Typically, ogres stand between nine and ten feet tall and can weigh up to 650 lbs. Their hides range from sickly yellow to a dull blackish-brown, with dark warty bumps, purple eyes, and black or orange teeth and talons. They dress in skins and furs, but keep their weapons reasonably well.
Ogres have powerful chiefs and sub-chiefs as the leaders of their tribe.
Ogre lairs are simple camps, where they keep their most precious belongings. This can include slaves, but most creatures are kept as food -- ogres devour halflings, elves and dwarves first of all, being fond of their taste, but they'll eat almost any humanoid given enough time.
Ogres mix freely with trolls, other giants, and orcs. They will also join with gnolls, and have been known to associate with clerics of gods of violence, war, and brutality, and as a result, they occasionally appear in demon armies as well (though typically as slaves).
Ogres are fond of halfling, dwarf, and elf flesh especially. As giants, ogres dwelling in the mountains and hills where dwarves live have been fighting them for millennia.
OD&D White Box
1e Monster Manual
2e Monstrous Manual
3e Monster Manual