Ettins were created at the tail end of the Third Orc Lord’s eugenics program. He was attempting to increase the intelligence of his ogre troops, and the magical mutation that did that also gave Ettins a second head, with its own personality.
Having two heads can be a curse more than a blessing for most ettins. The two ettin personalities can war and clash with each other, and not get anything done. More than one ettin has died because one of the personalities had their other head assassinated and promptly died from the wounds incurred from having said head killed.
However, for those ettins whose two personalities can work together, having two minds in one body can lead to a dangerous foe. The personalities can cover each others’ weaknesses with little effort, and they possess the tremendous strength that their ogre forebears have as well. Ettins can be surprisingly nimble, able to divide their attention among multiple adversaries with little difficulty and striking them down with lighting-fast strikes of the maces and clubs that they tend to favor.