Marwolaeth was a high priestess of necromancy, the Black Flame of the Universal Order of Death, and holder of the original Necromiconica. She was one of the only characters to live through all seasons of the show and existed in all the books in the universe. One of the original creators of the Necronauts, she perfected the art of cheating death... and sometimes even reversing it entirely. Which is fitting, since her name translates to "Death".
Her character is most often described as a Lawful Evil, with occasional lapses into Chaotic Evil just for the fun of it. This has been speculated to happen when she has performed too much necromatic magic for her system to handle.
No one knows her true age. She was born on the Isle of Mordedra to peasants who died of a plague before she reached the age of 10. She claims to no longer remember their names or have any feelings toward them, but it is often noted that she becomes withdrawn when the topic is mentioned. It is believed this is where her obsession with dead, and conquering death came from. Nothing else is known about her origins. It almost seems like she appeared out of thin air one day and all the Necronauts just acknowledged it.
In both the prequel books and shows she made grand shows of her powers of necromancy by performing feats believed to be impossible. However, those claims were mostly by men and she never took much stock in what men had to tell her about what she could or could not do. One particular notable occasion involved her raising multiple dinosaurs from the dead, including a t-rex and flock of pterodactyls, just to win a battle with an unnamed pirate king who told her to go back to the kitchen.
While she was always in command of whatever room she was in, she preferred to lead from the shadows. She never took the role of captain or admiral, as she liked the freedom to come and go between ships and places as she wished. Later in the series she developed the ability to travel through portals, but no one dared ask how she got that ability.