Thor
Asgardian physiology grants Thor near-invulnerability to physical damage. He has survived direct exposure to a dying star, sustained combat with the Hulk, and endured the full power of the Infinity Gauntlet. His regenerative capabilities allow recovery from wounds that would be fatal to virtually any other being.
Thor's documented survival incidents include nuclear-level explosions, planetary impacts, and concentrated cosmic energy. His durability ceiling appears to extend into the stellar damage threshold.