The main character, Mick St. John, was originally going to be called "Mike Angel". The name was changed so it would not be confused with Joss Whedon's vampire detective series Angel (1999). Similarly, the series title was originally going to be "Twilight", but the title was changed when Stephenie Meyer's book series "Twilight" became popular.
Sophia Myles (Beth) plays a woman who was saved and from her childhood watched over by never aging man she later showed interest in. In The Girl in the Fireplace (2006) she plays a similar role, only the man is not vampire Mick St. John but the Timelord called the Doctor.
Sophia Myles (Beth Turner) plays a vampire in "Underworld".
The trademark ring that Mick St. John always has on was hand-selected by Alex O'Loughlin from approximately 100 different choices created by a custom jeweler.
Beth's (Sophia Myles) last name is Turner - a tongue-in-cheek reference to a burning question in the story - "Turn her".