It is not uncommon for a powerful Wizard to pour some of their magical power into an artefact of some kind - something they can draw upon in times of great need. For most Wizards this usually takes the form of an amulet or more commonly a ring.
When the Wizard dies however, their power lives on within these treasures. When found by adventurers, these trinkets form a bond with their bearer, accentuating those attributes they consider most important.
However under certain circumstances it is not only the Wizard's power that lives on, but a portion of the person they once were; their 'soul' for want of a better term. Should the Wizard have turned to Chaos for instance, their warped nature can continue to live on through a new bearer.
Trogdar was granted such a ring by an animate statue. A golden ring with a single red gem, the ring immediately bonded to Trogdar, unable to be removed. It is perhaps unfortunate he chose not to wear it on his finger...
Whether the ring has exerted any influence over Trogdar remains to be seen.