Myrnin is a vampire and a scientist and he also becomes Claire's mentor in Midnight Alley. He is ancient, and in the further stages of the Vampire Sickness that is plauging the undead of Morganville.

Myrnin is a fan of Commedia dell'arte, even going to a dress up party as Pierrot. He also dressed Claire, his lab assistant, as a Harlequin. He tells Bishop that he always thought that Pierrot was the evil one.

He created Ada three hundred years ago, and has been arguing with the vampire computer ever since.

He has been working on a cure for the Vampire Sickness for several years, and every few years he takes a new assistant to help him. He has used human and vampire assistants, and during relapses he has killed at least five and has had at least seven, the two that are still alive are Claire and Dr Irene Anderson.

Though he and Claire have made breakthroughs with the cure, there have been times when they had no choice but to lock him in Morganville's underground vampire prison, or, on occasion, stake him. With the help of Claire he later discovers the cure using Bishop's blood.

During his episodes, he has threatened to bite or kill Claire, but during Fade Out he bit her. This was also after he was cured with Bishop's Blood.

There have been hints that he likes Claire more than as an assistant and in Last Breath it is quite clear about his feelings for her. In Bitter Blood Myrnin kissed Claire and she did not mind it, saying that she wasn't sure if she wanted to stop him.

He dresses in a random collection of clothing that includes vampire bunny slippers. He owns a pet spider by the name of Bob.

It is reveled in Myrnin's tale that he was Gwion's apprentice.

It has also been reveled that he is bi and had a relationship with Arthur Dee, an alchemist and son of John Dee.