|Out of universe information|
He was present during his kinds' war against the Lanteans thousands of years ago, where his Hive ship was damaged in the battle and forced to crash on a Human world where the Ancients had developed a dolmen-like device- powered by a Zero Point Module- that generated energy waves that weakened the Wraith's natural hostility and rendered them almost docile. Scar and his comrades would go into hibernation, sleeping for centuries until a rescue ship uncovered them, but none came.
One kingdom of Halcyonites discovered the sleeping ship and attempted to use the Wraith within as Hounds, the common shocktroopers in their wars against one another; Hounds were normally Wraith that had been captured during expeditions to other worlds, but the Hive Ship provided an unlimited 'free' supply of Wraith. Although this initially ensured the kingdoms' dominance over the other factions, the deactivation of the hibernation systems after then-Major John Sheppard killed the Wraith Keeper allowed more Wraith to awaken at a faster rate than the Halcyons could cope, one of which was Scar. During his attempt to escape to a Wraith Dart, he would be wounded by the king of the ruling Haylconite domain, which earnt him the name Scar for the deep wound across his eye.
Scar would be deposited in a reserve where wild members of his kind roamed and were hunted by the Humans as sport. Scar, however, was different and of a higher caste, resulting in him retaining enough of his intelligence to become a threat and led a group of his kind against the Halyconites. When Scar encountered the flagship team of the Atlantis expedition, he saw a way for freeing his kind; having shot Ronon Dex with his Particle magnum, he blackmailed Lt. Colonel John Sheppard by threatening Teyla Emmagan's life with the use of a Hound control collar, forcing Sheppard to destroy the Dolmen and free his brethren which began to wreak havoc of Halcyonite society.
However, although he subsequently retreated to the Wraith hive ship, taking it into space in an attempt to contact other hives, Scar's arrogance was his undoing; although he had shot Sheppard and Ronon, he failed to realise that Sheppard had been wearing body-armour that protected him from the bullets, and Ronon had set his gun to stun before Scar had taken it. With the Atlantis team pursuing him, Scar was defeated by Teyla Emmagan but activated a program Kefler, a Halcyon scientist had created to cause the hive ship to self-destruct in an attempt to take the team and the arriving Daedalus with him. Sheppard and Ronon killed him, but not before he was able to activate the program. Scar's hive ship was destroyed, but the Daedalus, while taking heavy damage from the explosion, survived due to upgrades to the Asgard shields. The Asgard engineer Hermiod was also able to beam every human out of Scar's ship before it exploded. (SGA: "Halcyon")