This person has a halo.
A halo is a ring of light that surrounds a person in art. They have been used in the iconography of many religions to indicate holy or sacred figures, and have at various periods also been used in images of rulers or heroes.
When perspective came to be considered essential, painters also changed the halo from an aura surrounding the head, always depicted as though seen full-on, to a flat golden disk or ring that appeared in perspective, floating above the heads of the saints, or vertically behind, sometimes transparent. This is the version often depicted in modern pop culture and art.