This post is in reply to Rayne's comment (December 8, 2010). At first I was going to answer with a comment of my own, but decided a post would be more appropriate.
Rayne asks: "I'm fascinated by a minor character growing into a major antagonist. How did this come about, and at which stage? How did Samael take over as antagonist? Did he do this gradually, by sneakily manipulating the author, or with a quick forceful coup?"
Knowing Samael's techniques, it was sneaky manipulation. LOL Seriously, though, Samael kept insisting I give him his own story. As the series developed and I continued my research, I realized his role was much bigger than I first thought. And it wasn't just about angels of death fighting against one of their own, it was about angels fighting against their oppressors.
The idea to make Samael the antagonist came about when I realized Xariel's role as an anti-hero wasn't working. I couldn't justify his actions and have the heroine, Karla Black, admire him for what he'd done. A murderous angel of death had better have a damn good reason for what he does if the audience is going to empathize with him. And in the first draft, that wasn't happening.
Since Samael is the one who wields the venomous rapier, I decided to have him retain it. But what motive would he have for killing humans and angels? And that's when I got the idea of having him become obsessed with getting his ex-lover Xariel back and threatening to kill when Xariel refuses to return. (Xariel's sex curse doesn't help, either.)
However, Samael's role has continued to grow throughout the second and third books and the position of the antagonist has shifted from him to the Seraphim. The pitch for the Angels of Death series: "What if the Seraphim, the highest ranking archangels, viewing love as the ultimate weakness, decide they are superior to God and create a world of intolerance and fear?"
According to some, Samael's name was originally Lucifer, the greatest archangel and Seraphim before the Fall. And this inspired me to play around with the idea of what if the Seraphim, fearful of Samael's return, order him destroyed but the angels of death rebel against them?
Samael is also an angel of death as well as chief of satans. According to Gustav Davidson's A Dictionary of Angels, Including the Fallen Angels, "Metatron is indeed the supreme angel of death, to whom God daily gives orders as to the souls to be 'taken' that day. These orders Metatron transmits to his subordinates Gabriel and Sammael." (Xariel formerly worked under Gabriel before being reassigned to Samael.)
So Samael moves from being antagonist to the role of inciting character. Antihero? Perhaps. But that's for another book.
My apologies for the long post. Also please remember this is a work of fiction and one of many ways this story can be told.