Paris was the mortal man that Zeus chose to judge the fairest of the goddesses - Athena, Aphrodite, and Hera.
Paris.
Zeus, as he gave the task to Paris.
Zeus' wife is Hera the goddess of woman and fertility. Hera was angry that Paris did not choose her but instead chose Aphrodite.
No god judged their beauty, the mortal chosen by Zeus to judge them was Paris.
The Trojon Was started when there was a beauty contest between Athena, Hera and Aphrodite. Zeus was the judge but couldn't choose. He picked a messenger called PAris to choose and he picked Aphrodite. She was so happy that she gave him a gift. The most beautiful girl in the country to be his. That girl was Helen. The husband of Helen was furious and wanted revenge on PAris. So he told all his men to go to Troy and killed him. That is how the Trojon War Started
Zeus asked Paris to judge the contest of beauty between the three major goddesses to win the golden apple of discord, if that's what you mean - the myth says that the Goddesses appeared to him at random to ask him to judge out of the three of them who was the Fairest - the apple said on it "To the fairest" - and the Goddesses attempted to ply him with gifts. Athena offered wisdom and skill in battle, Hera offered to make him King over Europe and Asia, and Aphrodite offered him the love of the most beautiful mortal woman, Helen of Sparta.
Zeus appointed Paris, the prince of Troy, to choose between Aphrodite, Athena, and Hera for the most beautiful. He chose Aphrodite, and was given Helen, which started the Trojan war.
It was the "will of Zeus" that the mortal Paris judge between the three goddesses, and chose the fairest according to Homer's version in The Iliad.
Zeus chose Paris because was the prince of Troy. He was a shepherd because his father once heard a prophecy that Paris would bring the fall of Troy
He did not judge Venus. Paris was the judge in a beuty contest between Venus, Juno and Minerva (or rather their greek counterparts). Venus won.
It was perhaps not a direct punishment to Thetis, the golden apple "for the fairest" was found by Hera, Aphrodite and Athena at her wedding and Paris was made to judge between them. His choice of Aphrodite began what would be the Trojan war when the goddess of love made Helen love Paris and follow him to Troy.