Scar was one of the three predators to enter the underground pyramid and would be the only one to leave alive. He was accompanied by his brothers Celtic and Chopper, and was the only one of the trio to achieve the rank of a Blooded Predator.
In the Movie
Scar is sent to the Artic with his two brother, Chopper and Celtic, to complete his Chiva (rite of passage) and kill off the humans on the hunting grounds when they become pesky by stealing their Plasma Casters, weapons that are required to complete their rites. They are able to kill a few before they even enter the underground, Scar in particular doing away with a human who tried to attack him with an ice pick.
While Celtic and Chopper are busy antagonizing humans, get sidetracked from their original goal, Scar goes his own way to find and kill Xenomorphs. He successfully bisects a facehugger before it can attach itself to his face, later killing another adult Xenomorph who thought it was being stealthy. However, as he takes off his mask to mark himself with the acidic blood of his quarry, a second facehugger attacks and infests him. Scar awakens some time later, and continues on, pursuing Alexa and Sebastian, the final two humans alive at this point. Sebastian is taken by a Xenomorph, leaving Alexa alone with Scar.
He looks to do her harm at first, but Alexa is submissive, begs for his help and returns his Plasma Caster to him. He still doesn't pay her much heed after that fact, until a Xenomorph attacks him and her throws it onto her. Surprisingly, Lex is able to kill the beast, intriguing Scar. Before anything more can happen, several more aliens attack, but armed with his Plasma Caster, Scar makes quick work of them and remaining ones retreat on their Queen's orders.
Scar, likely deciding that continuing on alone isn't a good idea, finally decides to ally with Lex for the time being. He arms her, making a makeshift spear and shield out of a Xenomorph corpse, then they move off to find Sebastian. He is already infested by the time they do, Scar moving to kill him, but Lex stops him and tearfully kills her friend instead. The Chestburster still emerges, Scar catching it and easily snapping it's fragile neck with his bare hand.
The pair are accosted by more aliens on the way to free, including Grid, but they've planted a Wrist Bomb to destroy all the aliens. They barely manage to escape it's blast radius, but once they do, Scar offers to mark Alexa as a true hunter for she has killed two Xenomorphs where his brothers could not even handle one. She accepts this mark and shortly after receiving them, both predator and human are faced with the Xenomorph Queen. Using the chains clinging to her body, they are able to tie her to a water tower and then send both her and the tower into the freezing water over the side of a cliff. Not before the Queen fatally impales Scar however.
Scar dies on Earth, in the snow, a young blooded predator with his human companion kneeling next to him. His body is taken onboard a Predator ship, where the Gunnison Predalien erupts from his chest.
While Chopper and Celtic were never far from each other, Scar was a bit of a lone wolf. He was efficient and honorable, unwilling to needlessly prolong a kill or hunt sick prey, until it attack him first. He also saw the value in having a partner once his own brothers were dead, and was considerate enough to arm Lex against any possible threats. Additionally, he seemed to show a sense of humor when he startled Lex by driving his dagger into the skinned head of a dead Xenomorph and causing its second mouth to pop out.
Even so, Scar, like his brothers, become suspicious with humans he and his brothers encountered as they arrived first in their hunting ground and stole their prized Plasma Casters not long before their arrival that resulting the situation become out of control. Because they unknowingly ruined their test on Earth, the predator become suspicious on humans even when they unharmed, as seen in his eventual confrontation with Lex where he challenged her a fight over stolen plasma caster on her backpack in spite of her have no weapon nor combat skills to defend herself, and still suspicious on her once he get what he wanted. In spite of his, upon seeing that Lex proved herself capable to defend herself by stabbed a xenomorph to death and realizing that they had to work together, Scar eventually recruit her to his side and even honored her for her contribution in fighting Xenomorphs.
Scar was rather unremarkable compared to his brothers, particularly his mask, which is rather simple in design. He is the only predator seen without his mask, his face having tiny black quills around his brow and jawline. Despite being a member of Yautja race, Scar's eyes were a very human brown.