Sammael is among the original and most powerful of Greater Demons, particularly a fallen angel of the highest order, along with Lucifer and Azazel. He is credited as a responsible party for the beginning of the Incursion.
Sammael was believed to have been created when the world began. He was once an angel, cast away from Heaven and became a Greater Demon, a general of Hell's army. He met Lilith, who eventually became his companion. He was believed to have taken the form of a great Serpent and tempted Adam and Eve in the Garden of Eden.
According to the legend, he and Lilith roamed freely, creating other, lesser demons. They mated with humans and created warlocks, and they were believed to have mated with angels to create faeries. Together, at around AD 1000, the pair performed a very powerful demonic ritual that could be performed only once and never again. The ritual affected Pandemonium and massively strengthened all of demonkind's resistance to the toxicity of the world of humans to them, as well as drastically weakened and thinned parts of the wards protecting the world from the Void, highlighting worn spots and creating holes in them. This allowed large numbers of demons to pour in from tears in the veil all over the world, attempting to devour the life around them. This event became known as the Incursion, the beginning of the period of a large-scale invasion of the world by demons.
This event prompted the eventual creation of the Nephilim. Because of this act, he was hunted down and slain by the archangel Michael with his sword, Glorious. He has not been seen either on Earth or in the Void for nearly a thousand years since, and is widely believed to be dead, or at least destroyed temporarily, only taking centuries to reform in the Void.
Sammael spent many centuries slowly reforming in the Void; trying to fight free of the darkness to rejoin his love, Lilith.
Around September 2007, Sammael was close to returning to full form and was looking for someone to help find him a realm to regain his power. He came to hear of the warlock Ragnor Fell and planned to reach out to him as the world's leading expert in dimensional magic. Ragnor caught wind of Sammael's interest in him and decided to fake his death and go underground.
About a month later, Sammael heard Lilith's painful scream as her form was destroyed by Simon Lewis's Mark of Cain. The power of her rage was enough to make Sammael regain his true form, though he was still unable to return to Earth. Lilith told him as she was fading the tale of her death and that she would be gone for quite some time. Upon hearing his beloved's story, he vowed two vows: that he would finish what he had started with the Incursion; and that he would personally see to it that the murderer of Lilith would suffer for his crimes.
Sometime after this he made contact with the warlock Shinyun Jung whom had kidnapped the warlock he was seeking, Ragnor Fell. Shinyun swore her fealty to him and he sent her to find the Svefnthorn and attune it to him. He had Shinyun stab Ragnor with it twice to grow his power and to force him to take the third thorning to prevent dying. Once stabbed three times, Ragnor was completely under his control and willing to do his bidding. Shinyun asked to be stabbed as well and he allowed it.
Ragnor eventually found a hell dimension for Sammael: Diyu—a Chinese Hell that used to torture souls before their rebirth. Sammael took the abandoned dimension as his own and claimed all its residents. He expected the dimension to work as it once had to be a dynamo of demonic energy, but because it had been abandoned for so long, it did not work. Instead of relying on the realm to manifest the energy he needed to return, he had to resort to other means. In 2012, Sammael had Shinyun and Ragnor buying spellbooks and components at the Shanghai Shadow Market to work a way around the Taxiarch's wards keeping him from Earth. He later had them steal the Book of the White from Magnus Bane to help towards these efforts.
Because Shinyun had made the decision to thorn Magnus—without Sammael's orders—he and his Shadowhunter friends, Alec and Isabelle Lightwood, Jace Herondale, Clary Fairchild, and Simon Lovelace (né Lewis), soon traveled to Diyu to stop their plans. As they came through the Portal, Sammael abducted Simon to torture him as revenge for destroying Lilith. His vendetta annoyed Shinyun as a silly distraction and made Shinyun question his power. She led the group to rescue Simon in an effort to get Sammael back on track. However, he became distracted once again after Magnus freed Ragnor from Sammael's power with the Heibai Wuchang. So, when Magnus was freed from the Svefnthron's power, Shinyun took the ball of power for herself and transformed into a Greater Demon. She took back her loyalty to Sammael as she believed him to be weak and dependent on others for power. She determined she would rule herself and began destroying Diyu. Sammael appeared unfazed by this turn of events; in fact he seemed amused. He promptly left Diyu to find another realm to claim.
In his human form, he appears as a young, slight man with a narrow face. He seems to dress in present-day mundane clothing with the exception of his green felt Tyrolean hat that has a foot-long golden phoenix feather stuck through the band.
- Chain of Gold (mentioned only)
- City of Fallen Angels (mentioned only)
- City of Heavenly Fire (mentioned only)
- The Lost Book of the White (first and only appearance)
- He is the second oldest of the nine Princes of Hell, the oldest being Lucifer.
- Sammael was the guardian of Esau and the patron demon of Rome.
- His name means "Venom of God" or "Poison of God".
- Sammael's will is tied to the Book of the White. As such, his servants feel a pull towards the book.