The Ring of Menegeld gives its wearer an incredibly long lifespan--making him nigh immortal. It is currently rumored to be in the possession of Malark Lester.
The ring of Menegeld is an ancient artifact dating back to the Netheril. It was created by the wizard Menegeld in order to extend his own life. He realized, however, that such an item would be sought after by unscrupulous persons of all sorts, and so enchanted it so that it could not be cut off. His plans did not work out the way he had hoped, however, so he was crushed a few years later in a freak accident with boulders. His apprentice inherited the ring, only to be poisoned a few months later. The ring passed from hand to hand, never staying on one long enough to be worthwhile. Its sensational history was made public in a book called The Many Deaths of Menegeld which is available in your local Beldin library.
The Ring was eventually found by an adventuring party (consisting of Yammato Khan Eininfar, Yomi Eininfar, Scythia Maya, and Ordin)somewhere in the Underdark. It was agreed at the time that Scythia would keep the artifact safe. Scythia was killed many years later by Ordin, who was getting old and feared death. He took the ring, blamed the death on Yammato Eininfar, and escaped when the town was soon after destroyed by a drow raiding party.
Ronin Eininfar pursued Ordin, determined to kill him in revenge for his parents' deaths. They both eventually ended up in Beldin, where Ronin killed Ordin and took the Ring. He kept it for several years, and was rumored to be nigh invulnerable.
Feyrin Raventalon, in his attempts to secure power for himself, tried several times to steal the Ring of Menegeld from Ronin. He eventuall succeeded with the use of a wish spell, but was thwarted by Vikii D'Vreeze, who magic missiled the Ring off of his finger. She then refused to give the Ring to anyone unless they gave her a kiss, so Mith Kaldaka kissed her, gave the Ring back to Ronin, and became Vikii's consort.
Ronin did not put the Ring back on. Vaune Nasadra convinced him to throw it over the Enclave cliff, since the thought of living so much longer than everyone else seemed to distress him. It was assumed that the Ring would land in Arvandor, and be safe from further involvment in Beldin affairs.
The Ring did not make it to Arvandor, however, but landed outside of the material plane location of the Eilistraean Enclave--the ocean. The witch Mystera found the Ring after much searching at the bottom of the sea floor. Whether she ever put it on or not is unclear, but it was somehow stolen from her some years later by Malark Lester.
During his brief riegn as King of Beldin, Malark managed to somehow duplicate the Ring's invulnerability powers and give them to his thirteen bodyguards. But before they ever entered the war, Malark and his retinue retreated from Beldin. Nothing has been heard of them since.