Character from the Marvel Comics universe
. He first appeared in Strange Tales #157.
The Living Tribunal is above all other entities in the Marvel Universe. He is the judge of the entire universe, and his decisions are final. He exists to maintain balance in the universe, which is why he lets bad things happen. His face is three-sided, with each side representing a different factor in his judgement. The exposed face through which he speaks (unless passing judgement) is Equity. The half-covered face is Revenge. The completely covered face is Necessity. He always ends his judgements speaking through Necessity, showing that he has made his decision.
The Living Tribunal only appears during times of impending cosmic imbalance, such as during The Infinity Gauntlet and The Infinity War. It is because of his judgement that the Infinity Gauntlet will no longer work. He stripped Adam Warlock of the Infinity Gauntlet, showing the magnitude of his power, since the Infinity Gauntlet basically makes you God. In the Marvel vs. DC miniseries, it was shown that the Living Tribunal was sort of an ambassador to the actual god of the Marvel Universe, which is presumably why he is so powerful.
As an end note, the cover of Pink Floyd's second album, A Saucerful of Secrets, has one of the Living Tribunal's faces in the upper-left corner, and Dr. Strange elsewhere on the cover.