Zilfur is a retired RuneScape player with a total level of 2,496. In 2010 Zilfur wrote a "Guide to efficiency" on the offical Runescape forums. This has helped many players to understand efficiency and become more efficient themselves. His knowledge and understanding of efficiency were monumental.
In addition to this, Zilfur quite notably has at least 20M experience in every skill on the game and was one of the more early players to achieve this.