Tantalus was the king of Tantalis, an ancient western Anatolian city he was named after. His father, Zeus offered him a spot at the Olympian table and he accepted. When he went to them, he stole nectar and ambrosia, brought it back to his people and revealed a secret of the gods. In doing so, he offered up his son Pelops as food for the gods. Only Demeter touched the food because she was distraught about her daughter, Persephone. She didn't know what it was and ate part of Pelops' shoulder. Zeus took the parts of the boy, put them together, and was able to bring him to life once more. He was given a bronze shoulder made by Hephaestus. In another myth, he stole a golden dog, made by Hephaestus, and gave the dog to his friend for safekeeping and later denied ever seeing it.
For his terrible crime, Tantalus was subjected to eternal starvation and thirst. He was made to stand in a lake with a fruit tree growing on the shore with fruit growing on a branch above him. Whenever Tantalus tried to drink, the water dried away and when he wanted to eat, a strong wind blew the fruits out of his reach.
As an addition, all male descendants of Tantalus were cursed whereas they are predestined to get murdered by a family member. This curse then continued straight to Agamemnon, the king of Mycenae and his family.