Sevotharte is the Prime Minister of Heaven (the White Angel). Technically, he is the Ruler of Heaven, since he controls all of Metatron's actions, and also acting as a guardian at the same time. Sevotharte never shows his face (dunno why?). He is truly the fallen angel, Laila, but has no memories of his past.
Laila was head of the Sandalphon project. Her best friend was Anael, but she was very jealous of her, because Laila was in love with Zaphikiel and Zaphikiel was in love with Anael. A group of men attacked and raped Laila, which drives her insane. She attacks Nydd Hogg, blaming him for what happened, even though he was innocent. Laila receives the mark of the fallen angel: Lilth. She goes to Sandalphon for help. All who were involved with the attack, including the innocents like Nydd Hogg, were killed (I think his wings were severed and he turned into a ghoul; in other words, he died). Sandalphon changes Laila into Sevotharte. As Sevotharte, she remembers nothing. She brings the death of Anael and the destruction of Zaphikiel (coincidence?). During the trial of Jibrille, Uriel brings the evidence that Zaphikiel collected to prove that Sevotharte is not really who he appears to be. Sevotharte finally remembers his past - being Laila, Nydd Hogg (who loved her), her best friend Anael (whom she had killed), and the reason for her change. Sandalphon possesses Metatron and rapes Sevotharte in order to create a body for himself, which only drives her even more insane (being raped was what caused her to become insane in the first place!). Nydd Hogg's spirit visits her and tells her that he still loves her, and does not blame her for his death. Sevotharte kills himself by jumping through the window, thwarting Sandalphon's plans for a body.
We are lead to believe that Sevotharte is a "he" throughout the story since he acts so much like a male, even though he still remains female. This is why I refer to Sevotharte as "he."
The dragon that guards the tree Yggdrasil. Nydd Hogg still remembers his love for Laila, and appears to her before she kills herself.