Celestial
The Celestials are an ancient race of powerful beings. Their origins are unknown, but the Collector has stated that he believes they predate even the oldest of the Elders of the Universe, and possibly predate the universe as it is currently known.
Celestials are capable of utilising the Infinity Stones without harm. Eson the Searcher was the last known holder of the Power Stone before it was discovered on Morag by Peter Quill.
Due to the incredible rarity of sightings, many in the Universe believe Celestials to be myths. However, Knowhere is built inside the decapitated head of a dead Celestial, and Ego the Living Planet proved to be the brain of a Celestial inside a planetary shell.
The only known instance of a Celestial interbreeding with any other species is Peter Quill, the son of Ego and a human woman. While Quill did possess some super-human abilities, these faded when Ego was killed, suggesting the abilities of Celestials cannot be permanently passed on.