The Seal of Solomon is a magical pendant created by King Solomon.
At some point, the Seal was created by King Solomon, possibly out of a meteorite. According to lore, King Solomon "commanded unto his priests bind my seal. But the jewel was of the cosmos." After King Solomon's death, the Seal was buried with the rest of his treasure in what would eventually become Israel.
In 1917, the Men of Letters located King Solomon's treasure in Israel and dug it up. Amongst the treasure, the Men of Letters found the Seal of Solomon which they described in their records as "a crystal that glowed with an unearthly light." The Men of Letters then transferred the Seal and the rest of Solomon's treasure to their chapter house in Portsmouth, Rhode Island.
In 1925, rogue Man of Letters Diego Avila decided to summon the gods Yokoth and Glythur from their alternate reality in order to cleanse the Earth and bring a new paradise. Diego and his followers used the Seal as part of a ritual to open a rift between the universes to bring the two gods to the Main Universe. After Yokoth consumed most of the Men of Letters present, the survivors closed the rift before Glythur could come through and the rest of the organization disavowed the incident and sealed the chapter house. The Seal was left in a secret compartment in the ritual room along with the ingredients needed to repeat the ritual.
In late 2017, Prophet Donatello Redfield learned of the ritual from the Demon Tablet. Corrupted by the tablet's power in his soulless state, Donatello first gave a fake ritual to the Winchesters and Castiel. Finally, Castiel forcibly removed the ritual from Donatello's mind and learned that they need the Blood of A Most Holy Man, Fruit of the Tree of Life, the Seal of Solomon and archangel grace for the ritual.
As Castiel searched in Syria for the Tree of Life, the Winchesters searched through the lore in the Men of Letters bunker but could find nothing on the Seal of Solomon. With no leads, they switched to searching for the Blood of A Most Holy Man.
Eventually, Sam found the lore stating that "the jewel was of the cosmos" and determined that it was likely a meteorite, but could find nothing beyond that at all in the lore. In desperation, the Winchesters searched through the bunker's archives until Dean finally found the records revealing the discovery of King Solomon's treasure and the Seal with it.
Having learned of the Seal's location, the Winchesters searched the Portsmouth chapter house, but had no luck in finding the Seal. Instead, they found Yokoth who they mistook for her vessel Sandy Porter and mistakenly set Yokoth free. After feeding, Yokoth captured Dean and took him back to the chapter house where she recovered the Seal and used it to reopen the rift to her world and summon Glythur. As Glythur attempted to possess Dean, Sam arrived with Marco and Ophelia Avila who attacked Yokoth. Getting his right hand free, Dean stole the Seal from Yokoth and tossed it to Ophelia who was able to use the Seal to close the rift, resulting in Yokoth and Glythur returning to their own universe.
In the aftermath, the Winchesters explained to the Avilas why they were seeking the Seal of Solomon. Ophelia gave the Winchesters the Seal and the siblings provided more detailed instructions on how to use it to open the rift. After receiving Gabriel's grace from Arthur Ketch, Sam was able to use the Seal in a ritual to open a rift to Apocalypse World that Dean and Arthur traveled through to rescue Mary Winchester and Jack.
After being stranded in Apocalypse World, Lucifer provided Michael with the ritual needed to reopen the rift. Lucifer listed the Seal, which he called "some glowy rock," as one of the things they would need.
- Season 13
- The Seal of Solomon appears to only act as a way to channel the power of the Demon Tablet Alternate Reality Rift Opening Ritual and isn't actually necessary if there is another means of channeling the ritual. In Beat the Devil, witch Rowena MacLeod channeled the ritual through her hands and didn't use the Seal. The rest of the ritual remained the same.