Personal identity, and a more subtle level of identity than either the Sun or Moon. Some say physical appearance, but I am not sold on that. The planet that rules the rising sign is a meaningful significator for you in your own natal chart and elsewhere. The ascendant represents your soul's journey, what you could call 'The Continuing Story of I Am Becoming'. The 1st house also represents the question itself in horary astrology; or the subject of the question.