Arzhul was a sidhe who challenged Meredith Gentry to a duel when she resided in the Unseelie sithen prior to the events of A Kiss of Shadows.

He tried to force her to shapeshift. Meredith, however, stabbed him, causing his death as a result of the shared blood that was part of the ritual of the duel before the duel started,  in effect he gained Meredith's mortality.

Meredith still has scars on her shoulder from his magical attack.

Referred to in A Kiss of Shadows.