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Urklyn was in his late teen years at the time of his death, with shaggy black hair and bright eyes just as his father had. He could be seen wearing a simple, light colored robe, a dress shirt and a pair of black pants, as was common among men during Reiss family gatherings. Unlike his family, he was of average height, like Frieda, and the tallest member.
In the year 842, Urklyn watched the death of his uncle Uri Reiss, who bequeathed the First King's power to Urklyn's sister, Frieda. When Frieda's Titan form tried to eat his uncle Uri, he was silently watching the whole scene with other Reiss family members, which excluded Florian Reiss, who was not in the scene. When Frieda arose from her Titan form, Urklyn ran along with the rest of the family to get her.
In the year 845, when Wall Maria crashed, Grisha Yeager invaded the Reiss chapel, turned into a Titan, and killed most of Reiss family members, including Urklyn. According to Rod Reiss, he was "finally crashed in Grisha's hand," while reaching out for his father.