The Ogre is a Horde Mode mini-boss.
He comes in the later waves of Horde, has high damage absorption, is very tall, wields an Ogre Club, a bigger and stronger variation of the Club, and you can get stunned even after parrying his attack, while also taking damage at the same time. It is recommended to use ranged weapons against such a foe, since running away after attacking will most likely not work, because of his great reach.
You can however exploit his ai by running towards him and instantly tuning around and running away. This will cause him to strike at you (wait for his grunting noise that indicates a swing) which will leave you with enought time to hit him once. After hitting him you should run away as soon as possible and start all over again. This will work way more easily if you manage to isolate him.
He has a damage reduction of 10, meaning he divides all damage taken by 10 (so a hit with an executioner sword, which would ordinarily deal 100 damage, deals a mere 10 damage).