Thetis is a goddess, who married king Peleus, who was a mortal man, as all men today. They have many sons, but just one became famous. His name is Achilles.
At the wedding of Thetis, Eris, the Great Lady came, and She thrown away golden apple of discord. Result of this was a battle between Athena, Hera, Eris' mother, and Aphrodite.