Thanks Salmor94, but we do not write your essay for you. However, here is some information that will assist you. The three most important people are Xeones (the protagonist), Paraleia (Alexandros' mother), and Dekton(bastard son).
Xeones is the main character and the reader watches as he assumes all of the known characteristics of a classic Spartan warrior. We see him struggle to understand and cope with the sacking of his city (to the point that he almost commits suicide). Apollo intervenes and encourages him to continue living. It is through Xeones' eyes that we see most of the story as it unfolds.
Dekton is the anti-Xeones, a foil as it were. His father was supposedly a Spartan hero, but did not claim him as a son as the mother was a captured woman from a conquered nation. He is treated like a slave and he resents it all of his life. From this are sown the seeds of revenge, anger, and deceit.
The Lady Paraleia is important in that she offers a different perspective on Spartan lifestyles. In their culture the women were there to simply breed strong children, preferably male, for the good of the nation. They had to watch as their children were taken from them at early ages and sent to train to be warriors. They are important, however, not only for the storyline, but to Leonidas. He states at one point that he chooses his legendary 300 based on the internal strength of their mothers. He was in particularly impressed with the Lady Paraleia in that she had cunning, intelligence, and her dedication to the country was also legendary.
Each affects the battle in different ways. Paraleia eventually comes into play because she is able to interrogate and find out when Xeones is lying. Xeones helps rally the troops during the final battle and understands why Apollo chose him to live when his city was sacked earlier. Dekton offers a glimpse into the darkness that is possible in the human soul and how if it can be harnassed and turned to a good use, that some redemption might be found.