If the Ascendant is in Leo, the Sun is considered its ruler; if it is in Virgo, Mercury. The astrologer then looks at which house that planet occupies and what angles it forms with other points. This is one thread for reading a chart, not another Sun sign or a quick personality description.
The system of rulers depends on the school. Mars is Scorpio’s traditional ruler, while some modern approaches use Pluto. So two astrologers can choose different starting points even when they work from the same birth details. It is useful to ask directly which system the reader is using.
There is a practical limit too: the Ascendant changes over the course of a day. Without a sufficiently precise birth time and place, its position cannot be calculated reliably, so its ruler cannot be named with confidence either. If those details are missing, it is more honest to leave the question open than to choose a planet based on a personality description. Within the tradition, this is an interpretive tool, not a test that decides who someone is.
The stars speak. The choice is yours.