Disambiguation: Ultra Boy / Reflecto / Emerald Dragon
First published in: 1962
Jo Nah first appeared as Ultra Boy in Superboy (DC, 1949 series) #98 (July 1962). His mind temporarily took over Superboy's body and they became Reflecto, beginning in The Legion of Super-Heroes (DC, 1980 series) #277 (July 1981). Jo became Emerald Dragon in Legion of Super-Heroes (DC, 1989 series) #55 (March 1994).
Link: https://en.wikipedia.org/wiki/Ultra_Boy