The Orcs were originally Aldmer worshippers of Trinimac who were changed into their current form at the same time Trinimac was changed into Malacath (or so the story goes). But the Aldmer may not have been the only worshippers of Trinimac. Recall the Imga, intelligent apes that are native to Valenwood and emulate the Altmer, whom they see as the pinacle of civilized culture. Assuming Imga already had a similar relationship to the Aldmer at the time of Trinimac's fall, it seems likely that a number of Imga would have taken up worship of Trinimac as well. When Trinimac became Malacath, his Aldmer worshippers lost much of their grace and intellect but increased tremendously in strength and toughness, becoming the brutish Orcs. If the same transformation were to occur to an intelligent ape–an already brutish creature–what do you think the end result would look like? I would imagine it would look a lot like an Ogre.
Of course, there is not real proof to this theory, but I think it makes sense. It would certainly explain the bond that Ogres have to Malacath. What do you all think? Does this seem reasonable to you?