Lilia -- the Princess of the Kingdom. She's a female character as Shakespeare woulda written if he was a feminist (as if): strong-willed, refusing to give up her birthright simply because she is female.
Armus -- son of Benvaltro, chief courtier to the deceased King. Betrothed to Lilia. To put it simply, not a nice guy; conceited, cruel towards Marcis on occasion.
Alexia -- widowed Queen, mother of Lilia and Marcis. Pushes betrothal between the above.
Marcis -- mad son of Alexia and the late Wilham. Older brother to Lilia; should have been King, but is obviously incapacitated due to being insane and all.
Wilham -- dead King. Not much more to say...
Benvaltro -- chief courtier to the deceased King; a Polonius-like character (from Hamlet), though infinitely more cunning. If I call him 'Benvolio' anywhere in the play, it's a typo. Mail me and tell me exactly where the typo is (Act #, Scene #, Line #), and I'll give you a cookie. Well, not really. But I'll be quite thankful.
Helva -- nurse to Marcis.
Yareena -- mother of Armus, and as nearly cunning as her husband.
...as well as various servants, commoners and some assassins thrown in for fun.