Cornelius Sigan's Jewel

Prior to his death, Cornelius Sigan transferred his soul into a heart-shaped jewel so that he could return from the dead.

Sigan's jewel was later found by knights of Camelot, and temporarily stolen by Cedric, who became possessed by the soul of Cornelius Sigan. Sigan's soul was later extracted from Cedric and returned to the jewel by Merlin.

Allusions
Sigan's jewel is similar to a horcrux in the Harry Potterverse.