Ogres are the traditional species enemies of the Goblins. Their current king is King Dimitar, who signed a treaty at the Peace Summit. Their capital is Ravagog, which was stolen from the gnomes and originally named Serenvale, back when King Gowg was ruling. Lady Cadence and Alvar have both studied them extensively.
The Ogre's ruler isn't decided by heritage or vote, but instead by fighting after the current ruler dies, to gain respect and obliterate any usurpers. Dimitar's daughter, Ro, and Bo both want to be the ruler. They are the ogres' strongest fighters, making them likely to succeed King Dimitar. Because of this and because King Dimitar didn't want them to fight, King Dimitar arranged a marriage between them. King Dimitar's hopes that only one of them would fight don't appear to be working.
The ogres are violent creatures, in general, considering that they have attacked both the former gnomish city of Serenvale and taken it and attacked a troll hive, destroying a generation of trolls. They train their children to be fighters from a very young age.
The ogres are not described very much in-series. If King Dimitar's appearance is anything to go by, ogres stand at about six feet tall. The ogre king looks a hairless gorilla (in Sophie's opinion) and has pointed teeth. Ro is described as having claws. All ogres seem to have gray skin, as King Dimitar's skin was described as being "like marble" and Bo was described as being able to blend into a rock so that Sophie didn't notice him at first. Ogres don't wear many clothes, their usual attire is metal battle armor.
While not necessarily friendly with the Council, especially after Sophie attempted to breach their king's mind, the ogres are not officially against the elves. King Dimitar states that the only ogres allied with the Neverseen are rebels. As stated above, the species hates goblins. During the Battle at Mount Everest, Sandor wrestled with one and the pair fell off a cliff. In Lodestar, King Dimitar signed a treaty agreeing that he would leave the elves alone, as long as they left him alone as well. This is broken when Sophie Foster and Keefe Sencen enter Ravagog to deliver him a note in Nightfall.
Ogres are great microbiologists. They have developed an enzyme called aromark, a tracker, which can be revealed using reveldust, and they hybridized a bacteria called Bucollosiscia, which can produce a lethal sedative called soporidine . They also engineered the plague on the gnomes, which could only be cured with Panakes blossoms. Apart from that, ogres also have prodigious strength, as one of them was able to hold off Sandor. All ogres can phase-shift, a method that after falling, can be used to launch themselves to safety using a special device. Ogres also can use an ogre mind trick that bring most elves to their knees in pain by transmitting a high-pitched frequency known as the Grusom-daj, though for some reason, Sophie is unaffected.