The Living Tribunal's true function - the task for which it was created - is to protect the worlds without end, to whom Earth is but a speck of dust. He safe-guards the multiverse from mystical imbalance and transcends the realms of death and eternity, order and chaos and all opposing realities. All the dimensions, each nebulous netherworld which exists either in time or in space - either as matter, or as fathomless void - such were given over into the eternal, deathless keeping of the Living Tribunal, by the Supreme Being of the Marvel Multiverse - the entity called by cosmic entities "the One-Above-All".
His half cloaked face represents vengeance, his cloaked face represents necessity and his full face represents equity. Everywhere in existence has the presence of the trinity. He uses all three faces to look upon the world and judge. He judges these dualities and must know their true nature. He could have a fourth face, which represents nothing. Mortal mutterings such as good and evil - right and wrong - have no meaning to such as the Living Tribunal.
The Living Tribunal was created jointly by Stan Lee, Marie Severin and Herb Trimpe first appearing in the Strange Tales title in June of 1967
Major Story Arcs
The Infinity Gauntlet is a gauntlet that contains the six Infinity Gems. Whoever possesses the Infinity Gauntlet gains virtual omnipotence, making the Infinity Gauntlet one of the most powerful artifacts of the Marvel Universe. The Living Tribunal has demonstrated power beyond that of the gauntlet on several occasions.
When Thanos got the Infinity Gauntlet, giving him all the powers of Power, Reality, Space, Time, the Mind, and the Soul, the Living Tribunal was the only one who was not affected by the will of the gauntlet. He was asked to empty the powers of the gauntlet because of the doom that Thanos might bring with it, and he refused to. This is to say that while the Living Tribunal had the power to he chose not to. After Thanos lost the gauntlet to Nebula, who lost it to Adam Warlock, the Living Tribunal was the only one who could stand up to the power wielded by the gauntlet.
Adam Warlock lost his temper during a trial, while Eternity was trying to prove his case that Adam Warlock was unfit to keep the Infinity Gauntlet in his possession to the Living Tribunal. When Adam Warlock lost his temper, his temper exploded, similar to a bomb going off with everyone being blown away from Adam Warlock.
Then, in an instant, the Living Tribunal said, "Let order be restored to this hearing." and everything was back in order, again proving power over (or mastery of without contact with) the Infinity Gems. The Living Tribunal eventually decreed that the combined power of the Infinity Gems could no longer be summoned by one person bearing the Infinity Gauntlet again.
Thus, the Infinity Watch was formed and the infinity gems were separated.
Escapades Across The Multiverse
Even as the aftermath of the Infinity Gauntlet incident was unfolding, The Living Tribunal was performing his standard duties across all of time and space. He sealed Earth-82432 off from the rest of the Multiverse in order to ensure that the Michael Korvac of that universe would never be able to escape and wreak the kind of havoc he had caused in his universe.
He later appeared on Earth-89112, a world devastated and corrupted by demonic forces and nearly destroyed it, thankfully by the time he arrived the Phoenix Force had already obliterated the demonic forces and restored order to Earth-89112. Upon sensing that the Phoenix Force had brought order back to that universe, he allowed it's existence to continue.
Then, in the Dimension of Manifestations, he oversaw the trial of an entity from Earth-691 known as The Prodigy and with the aid of a very enigmatic Celestial named Scathan the Approver sentenced him to death for his bold and childish attempt to disrupt the natural order of Creation by trying to take the One-Above-Us-All's place in the cosmos.
When Quasar brought the Star Brand artifact from Earth-148611 and accidentally passed it on to his girlfriend, Kayla Ballantine, the Living Tribunal became involved in a conflict over the Star Brand which resulted in the Stranger bringing Earth-616 and Earth-148611 together in the same reality as part of one of his experiments.
After the conflict was over, The Living Tribunal took Kayla into custody for disrupting the balance of power in the multiverse and sentenced her to live the rest of her days in exile on Earth-148611, which he then sealed off from the rest of creation in order to prevent a disaster like this from occurring ever again.
Dc Vs Marvel (Non-Canon Event)
Two extremely powerful entities called The Brothers attempted to obliterate the Marvel and DC multiverses, The Living Tribunal teamed up with The Spectre in order to prevent them from doing just that. At one point, the Living Tribunal and the Spectre managed to save both multiverses by fusing them into a single reality but the Brothers eventually separated back into two individual beings forcing them to take the Brothers head on.
Unfortunately, their attempts to stop them simply weren't enough and both were nearly destroyed, thankfully Access, the human successor to a man who once maintained the balance between the two multiverses via the Nexus of All Realities was able to stop the Brothers. But even so, the Living Tribunal and the Spectre continued to remain in contact and kept a close eye on both the Brothers and Access, whom they did not trust with such gravely important matters like maintaining balance between realities let alone two multiverses.
When Thanos and Adam Warlock teamed up to defeat the Magus, Thanos suggested Warlock use the Infinity Gauntlet. But to their surprise, it would not work. The Living Tribunal had taken away the power of the gems when together. Galactus went to have a hearing with the Tribunal to restore their power. The Tribunal claimed the decision should be made by Eternity, who was in a catatonic state.
Galactus was able to get Eternity to speak with the use of Gamora and the power was restored. But they unknowingly restored the power when Magus had obtained the gauntlet. After Magus' defeat, the power of the gems together was once again removed, never under any circumstance to be reinstated.
The Final Escapades
After the war, the Living Tribunal went back to performing his duties during which he hired She-Hulk to be his apprentice and a member of his Magistrati, who oversaw the judgement of events that he considered to be beneath him, he also came to her with many dilemmas including a decision which could have made Earth-1610 the new heart of the Multiverse and could have lead to the destruction of Earth-616.
He later opposed the Galactus of Earth-982 and joined forces with the other major cosmic deities native to that universe in an attempt to stop Galactus from igniting a new big bang, but their combined attack was repelled by the world devourer who was later defeated by The Silver Surfer. With Galactus now a part of the Surfer, the Living Tribunal left Earth-982.
When Earth-616's Odin died, it was felt across all of time and space and briefly caught The Living Tribunal's attention. Giant Man briefly took Crusher Creel, the Absorbing Man, to the Dimension of Manifestations where they were both exposed to the mind-breaking experience of seeing The Living Tribunal, The In-Betweener, Lord Order and Master Chaos standing together in an "unfiltered" portion of the Dimension of Manifestations that could drive mortals insane if they remained longer than two seconds.
The Living Tribunal was found dead by Iron Man and Uatu the Watcher somewhere in deep space, the cause of his death is currently unknown as are the circumstances which lead to his demise.
Powers and Abilities
The Living Tribunal possesses limitless power, able to erase entire realities from existence. He has no free will, bound to the wishes of his only master: The One Above All. He is nigh omnipresent, and has power that can shade the likes of Oblivion.
The Living Tribunal is the second most powerful being in the Marvel Universe, only surpassed by The One-Above-All (not the Celestial). For reference see the All-New Official Handbook of the Marvel Universe A-Z #6.
The Living Tribunal has no counterparts as he is nigh omnipresent and thus simultaneously exists in all realities and time periods. He has ventured to parallel universes before, but his unique nature prevents those realities from duplicating him, as it would severely disrupt the space-time continuum.