Originally introduced in J.R.R. Tolkien's classic "The Lord of the Rings," the ringwraiths gained increasing popularity with the release of the film franchise. First seen on film in "The Lord of the Rings: The Fellowship of the Ring," the ringwraiths are mysterious and threatening dark spectres. Their back story as greedy human kings who accepted the evil Lord Sauron's gifts and were subsequently enslaved leading to a half-life of near immortality increases their eerie reputation. Through most of the trilogy they appear in their "black rider" guise, hooded and armoured astride giant black horses and later flying beasts.
Purchase or sew a black under robe. Beneath their outer robes, the ringwraiths or Nazgul wear a long loose fitting black robe or dress. It should stretch from your shoulders to the ground and have no front clasps or closures. In a pinch, a long-sleeved black crew neck T-shirt and a floor length, plain black skirt would work.
Buy or sew a large black outer robe. Some costume shops will sell something workable in a costume package for the grim reaper. For the most accurate version you will have to sew your own. Use thick coarse black material to sew a basic open robe. Don't hem the ends and unravel them a bit to make them look ragged.
Take two yards of the fabric you used to make your outer robe and drape it low over your face and head. Ringwraiths don't have a real hood attached to their robes. Instead, their heads are covered by a large piece of the same fabric their robes are made from. If the front edge of your fabric hangs too limply you can sew wire into a hem and use it to shape the front.
Distress the edges of your robe and hood. Ringwraiths were on the road for a long time hunting the One Ring so their clothing is threadbare and worn. Distress the edges by unravelling them, staining them and scoring them with sandpaper. Unravel a few threads so the edges are ragged.
Add black mesh fabric to hide your face for a creepy, mysterious effect. Black mesh fabric is thin enough that you can see through it easily but it obscures your facial features. Either sew black mesh fabric around the opening of you draped bonnet or wear a black mesh face mask under the hood.
Make gauntlets. Ringwraiths wear armour beneath their robes, the only visible parts of which are their gauntlets or armoured gloves. You can achieve the look of gauntlets with fabric paint on black gloves or by using fabric glue to adhere silver or grey felt to black gloves.
Wear black shoes or boots. Ringwraiths seem to almost glide along the ground. To achieve this effect your shoes should blend in with your costume.
Wear a toy sword on a belt underneath your outer robe. Glue or tie the scabbard onto a belt; if the sword does not come with a scabbard you can simply slide the sword between your belt and your body.
If your toy sword looks too plastic you can spray paint it with a matt silver or grey paint for a less obvious look. For a costume like the Witch King of Angmar, leader of the ringwraiths, wear your hood down and recreate the Witch King's mask and crown with tin foil.
Make sure the black mesh fabric has a loose enough weave that you can see through it easily. If you are going to be in a situation where you will need totally unobstructed vision, skip the black mesh.