A man who owns the largest collection of living things in the galaxy and treats every one of them as an exhibit.
Taneleer Tivan is the keeper of the largest collection of interstellar fauna, relics and species in the galaxy, working out of the mining colony at Knowhere. He is the Grandmaster’s brother.
He exists in these films for one structural reason and does it very well: he is the man who explains the Infinity Stones. In 2013, Sif and Volstagg bring him the Reality Stone for safekeeping, on the argument that keeping two Stones in one vault is foolish, and Guardians of the Galaxy has him narrate the whole history of the Stones to a group of people who have just stolen one.
Minor spoiler
His assistant destroys the Power Stone’s containment in Guardians, and his collection with it. In Infinity War Thanos arrives for the Reality Stone, and what the Guardians walk into on Knowhere is not what it appears to be.