Ulklin was a boy in his late teen years at the time of his death, with dark brown hair and light brown eyes. 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.
In the year 842, Ulklin, along with the rest of the Reiss family witnessed his sister Frieda inherit the Founding Titan from their paternal uncle Uri and comforted his younger siblings Dirk and Florian who were shocked by the scene.
In the year 845, after the Fall of Wall Maria, Grisha Jaeger invaded the Reiss chapel, turned into a Titan, and killed most of the Reiss family members, including Ulklin. According to Rod Reiss, he was "finally squeezed in Grisha's hand", while reaching out for his father.