Rex is the son of UnderWar Mettaton and Undyne. He ran was stolen by Gaster at birth and he extracted his determination and gave it to Undyne (She did not know it was her son's DT because she did not now where he was). Gaster also tortured him by pulling on his head and legs so hard he started to get 1.5in deep scars all over. He has one 3in deep and 5 inches wide over his where his eye should be. Also he was given chinese water torture (Google it) and was driven mad. Gaster once made an invention that put a laser in your ear and got rid of the dead skin cells and ear wax and prevents it from coming back. He also did it to his nose, hands, feet, he also enhanced his eyesight, and gave him sharp nails and toe nails for climbing, fighting, lockpicking, etc. One day he escaped from the lab and now he is Neutral bounty hunter, but prefers working for the Humans.