The Living Tribunal is a vastly cosmically powerful humanoid entity, and is a multiversal cosmic being created by the One-Above-All. He is the second most powerful being in the Multiverse, having supreme authority over the Primordials and all Abstracts, and only surpassed by the One-Above-All.
In all realities, the Living Tribunal manifests as a Guardian of the realities, protecting each one from threats that causes imbalances between the realities, and mystical extra-dimensional distortions. The Living Tribunal is also the embodiment of Justice in the Multiverse.
Even through he's a singular entity, in his manifestations in a reality, each one of his manifestations takes a different personality, act, or behavior in each reality, in a act to be like a multiple being, when he is actually just a singular entity.