Scar is a disturbed loner. His right arm does not belong to him but his brother. His brother was obsessed with finding the Philosophers Stone and tattooed his whole body. During the Ishbal civil war... Scar seeks his revenge against the state alchemists all of whom he blames for the destruction of Ishbal. His wrath does not extend however to nonstate alchemists which is why he does not seek to kill Alphonse Elric during their frequent confrontations.