The Gilbert Rings protect people from being killed by supernatural beings or causes, as long as the rings are worn.
The Gilbert Rings are worn by the Gilbert men usually, but there has been one female shown to have worn a Gilbert Ring, (who had the original Gilbert Ring and passed it down to her future descendants) Samantha Gilbert.
However, the rings can be cut off or forcibly taken off, and then the person wearing it can be killed. Grayson and John Gilbert inherited the rings from their father. John gave his own ring to Isobel, who then gave it to Alaric. John then took possession of Grayson's ring after the latter's death. There are only two known Gilbert Rings in existence. Both rings are made with black stones. Alaric and John's former ring is now bound to the last White Oak Stake, making it indestructible, leaving only one known ring left. Nadia Petrova also refers to the rings as Invincibility Rings in Original Sin.
Emily Bennett had enchanted these rings in 1864 and gave them to Johnathan Gilbert, who passed it down to his descendants. It is unknown if she knew the ill effects of the ring.
The first time is seen to been used is when Damon stabs Alaric with a stake in A Few Good Men, and not soon after he comes back to life. The next time is when Damon snaps John's neck and throws him off the roof of the Founder's Hall in Under Control. Alaric offered to take off his ring and let Isobel do whatever she wanted with him when she came into town, but she decided not to kill him.
Katherine cut off John's ring and stabbed him in Founder's Day. He was taken to the hospital, and when Elena and Stefan visited him, she gave his ring back to him. Stefan had a talk with John and he force fed John some of his blood, and threatened him, saying to leave town or he would kill him so he could turn and hate himself. The blood healed him and before he left town and visited the Gilbert House. Jeremy later catches Damon trying to kiss Elena and since Elena refused to kiss him back, he runs over to Jeremy and snaps his neck. After Damon leaves, it was revealed that John had given his ring to Jeremy and later Jeremy came back to life.
After his return, John took possession of Alaric's ring under the threat of telling Jenna the truth about vampires. When Elena dies in the hands of Klaus, John sacrificed himself to bring her back to life and left her the ring to give to her own child someday but she allows Alaric to have it until then.
After Alaric was killed multiple times, he became insane and developed a split personality. He later worked with Esther to create an indestructible White Oak Stake, by melting one of the rings.
In We All Go A Little Mad Sometimes, Jeremy's ring brought him back to life after he had been killed by Elena when she fell victim to the Hunter's Curse, hallucinating that he was Connor Jordan. This was the last time Jeremy's ring would work on him after activating his Hunter's Mark and powers, making him a supernatural human.
In Down the Rabbit Hole, Jeremy's neck was snapped by the immortal, Silas. Immediately after, inStand By Me, it was revealed that since Jeremy had become a member of The Five, he had technically become supernatural so the ring's effects no longer worked on him despite Elena's hope that it would. Overwhelmed by her brother's death, she decided to burn down their house to create a cover story, throwing the ring to Damon before setting the house ablaze.
In She's Come Undone, it is revealed that Matt was wearing the ring when Damon killed him to provoke emotions into Elena. It is unknown if Damon gave Matt the ring to keep, or if he simply lent it to him. Though it was likely that Damon only gave it to him after he and Stefan arrived to where Elena and Matt were, otherwise Elena would have noticed Matt wearing it.
In Graduation, it is shown that Matt is still wearing the ring, suggesting that Damon may have let him keep it.
In True Lies, Matt is killed by Silas while wearing the Gilbert Ring & awakens on The Other Side where he meets Bonnie and she explains why it takes longer for a person to resurrect each time they die. When a person is killed with the ring on, they reawaken away from their body on The Other Side, and to return to life, they must find their way back to their bodies. Each time they die, they awaken further and further away from their bodies, which is why they take longer to return to life. When they eventually resurrect, they have no recollection of their time on The Other Side.
After the Other Side begins imploding, Matt was then able to remember his encounters with the spirits of Vicki and Kol upon resurrecting. As the ring works by bringing a human to the Other Side while their body heals before their spirit reconnects with it, it is unknown if the ring can continue to work as the Other Side is now destroyed, possibly rendering the ring useless.
The ring was originally charmed by Emily Bennett, though it is unknown if they actually belonged to her, or she just used her magic on them. It is known that Johnathan Gilbert was the first member of the Gilbert Family to possess and use the ring in 1864, and it has been passed down the Gilbert Family since then.
Damon Salvatore (had the last remaining ring, given by Elena after Jeremy's death.but he doesn't use because Damon is a vampire)
Matt Donovan (Currently owns the last remaining ring, given by Damon.)
The rings can bring back to life humans killed by the supernatural beings (Vampires, Werewolves, Doppelgängers, Hybrids, Ghosts, etc.). Even when the human is killed indirectly, by use of an object (gun, knives, cars, etc..) the wearer can return to life. The ring cannot bring the wearer back to life if their death is 'natural', i.e. caused by another human, natural disaster or disease. The resurrection time varies from minutes to hours. Alaric was killed by Damon but returns to life in minutes, but when he is hit by Tony, Alaric returns to life hours after (and in this particular incident, the wounds sustained were not completely healed).
The magic of resurrection used consistently damages the psyche (totality of the human mind, conscious and unconscious) of a human, causing the ring to make a person go crazy (The Darkness), to the point of having no memories of his/her actions during a given time limit. The more the ring was used, the effect increased considerably. In 1912, Samantha Gilbert was the previous owner of Alaric's Gilbert Ring, she became a killer, implied that Samantha died and was resurrected multiple times like Alaric. The ring began to have effects on her brain and she wrote in her Gilbert Journal that she couldn't control herself. Alaric admits to feeling similarly about having gaps in his memories. Meredith said that Alaric might have been killing the Founders members and not remembering it. Elena confirms it after having read Samantha's journal. In a flashback at the end of the episode, 1912, it shows a Founder being murdered by Samantha, who is wearing her Gilbert Ring. However, it is revealed in Break On Through that these side effects can happen even if the person is not wearing the ring.
Originally it was thought that the damage done to the psyche of the resurrected was done by the ring itself as a side-effect. However, it was revealed by Esther that the ring simply leaves one vulnerable to manipulation by the spirits on the other side, as she was the one to manipulate Alaric in order to bring out his hatred of vampires and make it so powerful that it created a split personality.
John's ring as it was first seen.
Isobel holding a ring.
John's ring cut off when Katherine was acting as Elena.
Scott Kay "Gilbert" ring Black Onyx set in hand graved Sterling Silver.
In Masquerade, Jeremy tries to give his ring to Elena to stop the curse of Lucy but she refused so its left unknown if the rings can or not protect people from witches spells or if it can protect the doppelganger.
When Jeremy offers his ring to Bonnie she jokes that he was asking her to go steady.
Both known Gilbert Rings are made by world renown jeweler artisan Scott Kay. Both rings can be purchased for under $500 each. The ring in this wiki is available on tribalhollywood.com.
The effect caused by the rings is the loss of memory, and extremely dangerous and insane actions to kill.
The effect is the mirror of the actions and personalities of Klaus and Katherine von Swartzchild in the Original Series.
After the Hunter's Mark appeared on Jeremy, the ring continued to work as when Elena killed him in her Hunter's Curse hallucinations, only becoming useless to Jeremy after activating his Hunter's powers by killing a hybrid as they were half vampire.
The rings' negative side-effect is that while on the Other Side, no matter how briefly, the souls of the wearers are vulnerable to manipulation by the spirits dwelling there
Despite The Gilbert Rings being passed to the eldest Gilbert Son, Samantha had one despite her sex, most likely inherited from her father or grandfather Johnathan to protect her from the Supernatural since she knew about the Supernatural.
Alaric first felt the negative effects of the Gilbert Ring after his fourth death; when he was run-over.
Damon is the first and only vampire to own a Gilbert Ring, not counting Isobel, Alaric and Elena, who all became vampires after they gave up the ring.
The fact that neither any member of The Original Family, nor Katherine Pierce were surprised by the ring suggests that other rings (or other jewelry) with similar powers also exist, and that they have encountered other people over the centuries who have possessed these rings (or other jewelry). It is also very likely that Emily was not the only witch with the power to make these rings, which supports this theory.
Now that the Other Side has been destroyed, it is unknown if the rings will continue to function.