Writers are always looking for ways to make their characters come alive. An interesting and effective method is to cast the horoscope of the character based on key personality elements being established by particular astrological aspects - preferably heavy planet aspects. By determining the approximate birth year of the character being studied (birth year as though he/she were a real person - not necessarily the year the actor was born.) and locating the dates within that time frame the particular aspect took place, a hypothetical birth date can be established for the casting of a natal horoscope.
One of the fascinating aspects of this process is how complex the character can become. Since no astrological aspect exists alone, using a key aspect to establish the chart brings with it all the varying, and sometimes contradictory, information one finds in the chart of the real person.
When dealing with a group of inter-related characters, establishing the chart of the lead character is of prime importance since most of the other characters can then be defined through their psychological relationship to the lead. For instance, if the lead character is a difficult, cantankerous pill but his best friend loves him like a brother, the best friend's chart needs to include the capacity to love the lead character. This aspect of the friend's personality may need to be a key feature of his chart.
When the character is one that has been played by an actor, it is often helpful to work up the chart of the actor as well. Since the actor personified the character, it seems appropriate for something of the actor to be reflected in the character. This is most easily accomplished by using the actor"s sun sign or ascendant as the character's ascendant.
Some books on the subject: Astrology