Zilfur is a RuneScape player who had a total level of 2,496 when he took a break in 2012. In 2010, Zilfur wrote a "Guide to Efficiency" on the official 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 had at least 20M+ experience in every skill on the game up to and including the Dungeoneering skill and was one of the more early players to achieve this feat. Upon release of the Completionist cape in May 2011, Zilfur was one of the first players to claim this cape.
After Zarfot, Zilfur is arguably the 2nd most efficient player to ever play the game.
In 2020, Zilfur returned to the game and quickly obtained the new maximum total level of 2,898. He has also obtained 200M XP in twelve skills and has several others with over 100M XP. It's anticipated that he will train these to 200M XP as well. Zilfur has said that his ultimate goal would be 200M XP in all skills, but he doesn't know if he could ever invest enough game time for this, so just continues to play the game whilst he enjoys it.
Zilfur currently has an overall XP of over 4 Billion and an average XP rate of ~358K XP/hr. Having originally started his account in 2005, this makes this feat all the more impressive. This is the highest known XP/hr of any account ever created and Zilfur is constantly increasing this number on his way to maximum XP.