One of my all time favorites and one which has probably undergone as many variants as any fly created.
The original was tied by Frank Sawyer, a river keeper on the Wiltshire Avon.
His materials were:
Hook: #12-#24, 2XL Round or Perfect bend
Thread/weight: fine dark colored (enamelled) copper wire
Tail/abdomen/thorax/wingcase: red/brown fibers from a cock pheasant center tail feather, to match the copper wire in color. Some writers insist that only the center tail feather will yield the correct quality of fibres.
Simple, elegant and absolutely deadly