Tamlin

Tamlin was either an ethereal or a dreamshade tithed to Hell by the fae. Although he claims to have originally been a man, his time among the Fair Folk and the subsequent infusion of fell energies has more or less guaranteed that he shall never wear such a form again (though he does enjoy faking it for “conquests” of his own).
Seir rides Tamlin now, but it is the erstwhile knight’s lot to become the Stallion of the White Horseman whenever one is named.