Ethiopian bulls were supposed to be enormous bulls—twice the size of regular bulls, with red hides and blue eyes. They were also supposed to have horns that they could move as easily as ears. They were said to be impervious to steel, with thistles on their hides that deflected all weapons. The only way to catch an Ethiopian bull was to dig a pit and lure it in, and then wait for the creature to die.
It’s believed that this legend came from early sightings of African buffalo. I’ve recently come across a slightly re-imagined Ethiopian bulls in the Percy Jackson series, where the bulls are actually built by Hephaestus, the god of metals and blacksmithing.
*image from here.