He was just another British Empire pawn, making his moves to steal something precious for the king. Elgin, whose name has given the English language a synonym for "vandal" and "thief," had a long imperious title and birth-name not worth repeating. The only name for which he is remembered is the one associated with the near-destruction of the Parthenon, one of the great monuments of Grecian civilization and all human heritage. He wanted to help decorate the newly christened "United Kingdom of Great Britain and Ireland," founded by Act of Union in the same year Elgin began removing the ancient statuary. A group that has been working to undo that wrong by a man whom Lord Byron called at the time "a dishonest and rapacious vandal," has expressed solidarity with the work being done to get the Gal Gréine out of a British war museum, and returned to Dublin, whence it was stolen in 1916. You can read about the Gal Gréine controversy here.
Elgin came to ownership of the marble statuary, which he had removed from Athen's great temple on the Acropolis by dubious means. The marbles depict scenes from Greek history and mythology without clear description of their meaning. Some believe the frieze depicts the founding of the city of Athens, others that it represents a ceremonial procession associated with Elegian mysteries. Gods such as Zeus, Apollo and Poseidon can be can be read in the statuary. Elgin dismantled this great cite of human heritage in the first decade of 19th century, and was able only to haul about half of the Greek treasure to the expanding British capital.
Greece was under the foot of the Ottoman Empire at the time of the removal, and Lord Byron was among the great advocates of Grecian independence, which happened in a way in 1830 when the Ottomans were driven out. The legality upon which Elgin obtained the marbles was a supposed purchase he swore to have made with the Ottoman authorities, but which scholars such Professor David Rudenstine of the Benjamin N. Cardozo School of Law concluded "is certainly not established and may well be false".