Surya (the Sun)
The Sun represents the soul, the ego and the body of the individual, and therefore its placement is of great importance. The Sun is best placed in Mesha (Aries) where it is called exalted. Opposite from there, in Tula (Libra) it is least auspicious and called debilitated. The sun is lord of the sign Simha (Leo) and also of the house where Simha is located.
Parashara's Light will provide you with all of the details on the placement of the sun in your chart and how it affects you.