If you are fortunate enough to live near a body of water that contains King Salmon I would suggest you go try to catch them... Hooking, fighting, and landing these massive fish is an adventure you will not forget.
The flies I use for Kings are very simple. Large wooly buggers in assorted colors do the trick, I personally like pink, red, purple, and chartreuse. If you want a high chance of Kings actually taking the fly (as opposed to sight fishing aka lining) stay off the gravel and stick to deeper pools and runs where the fish can't see you, and you can't see them. Drifting along the bottom, or swinging will elicit fair strikes, and a fight you will not forget!
King salmon fights usually take a great amount of effort for the angler and the fish. Even though these fish are destined for death, handle and revive them properly so they have a chance of spawning. Using a net will avoid the fish from damaging flops on the shore, and it will also allow you to keep the fish in the water. A lengthy revival may be needed, so take your time and make sure the fish can swim away with full strength.