Generally. the sapient species of Mundus fall under three main categories: Mer (or elves, including Orcs) Men (humans) and Beastfolk (although some Beastfolk may have once been men or mer). However, there are two species intelligent enough to use tools and clothing: Ogres and Goblins (some Goblins can even do magic!). They both are somewhat similar in that they have connections with Malacath(although this may just be because they are both outcasts), and despite being somewhat intelligent, their souls can be trapped in normal soul gems instead of just black ones.

They bear little resemblance to humans due to their pointed ears, in the case of the Ogres their size, their skin tones, and their sharp teeth. Likewise, they look barely anything like elves (far less than even Orcs do). They then could be classified as beastfolk, but all other beastfolk have some sort of resemblance to a normal animal, while Goblins and Ogres do not.

So, what are they? Some mer/men so mutated from the original that they make Orcs look like Aldmer? Beastfolk that happen to resemble some non-existent animal? Some sort of non-sapient monster risen to primitive sapience to serve as better slaves for the Altmer? Or some strange creation of Malacath's?

Goblins are rejected altmer used for slave labor, instead of being killed, while the ogres are the goblin slaves that followed the Trinimac followers who then became the orsimer.

Actually, I'm not sure. There hasn't really been any solid info about the origins of goblins and ogres...or really anything in general, other than being monsters to kill. If ears have anything to do with it, gobbos seem to be related to mer, somehow. However, I doubt you'll ever hear of a mer admitting to being related to goblins.

According to Raga lore, Goblin's originated from another dimension and used to be huge, but were defeated by Divad Hunding, who shrunk them to their current size.

I wanted to say that, but I didn't want to pull it out, as I forgot where I found that. Thanks, Tidus.

http://www.imperial-library.info/content/daggerfall-compilation-redguard-history here's the general link to the Imperial Library where I found it

According to that same book, "Redguards" are called such because they arrived in Tamriel covered in blood. I'm a bit hesitant to admit it as fact. I've heard someone rewriting the legend with Trinimac's anus as the interdimentioal rift and the giant goblins as Orcs.

Ogres, and all other creatures, plants, etc., are descendants of the et'ada. Yffre stabilized everyone's forms, and some unlucky saps were stuck as Orgres (or mushrooms) while others got to be cool elves.

I would assume that was referring to the fact that they came in and slaughtered everything in their path, but that's just my first impression. Note we also have two different invasion of giant goblins from another dimension, from two different Raga sources at that, of course this is all legend. ;p