The perfect dry fly for trout would be high-floating, durable, simple to tie, and almost universally effective. The Elk Hair Caddis is notable for all those reasons, and a few more. The pattern is usually thought of as a Western style, but it was first tied by Al Troth in Pennsylvania in the 1950s. Troth later gained fame as a Montana fly tyer and trout guide, and his new dry fly first came into wide use along turbulent trout rivers in the Rockies. It has produced well for me on trout waters from Alaska to Ireland. Now it's a global standard.