Heathcliff

He is the owner of the unique skill "Holy Sword" and is considered to be strongest player in-game. He wields the one-handed sword and a tower shield collectively called as Liberator. He also was able to hold off the boss of the fiftieth level for ten minutes by himself, which earned him the title "Man of Legend". It is also rumored in SAO that Heathcliff's health has never gone into the yellow zone.

(Source: swordartonline.wikia)