Elite Black Knights are a fairly unknown NPC. They can be found by going to the task tab, and then under monster teleports, click on Elites. They are a level 138, and are probably known best for their ability to drop saradomin swords. Although this is rare, they are farily easy to kill, and a saradomin sword is 55,000,000GP. You can also get Elite Black armor, but is fairly cheap, and not worth the time it takes to get it.