Which Titan was punished by holding up the sky?

Atlas was the Titan punished by Zeus to hold up the sky.

Atlas was a son of the Titan Iapetus and the Oceanid Asia or Clymene, and a brother of Prometheus, Epimetheus, and Menoetius. During the Titanomachy, Atlas fought on Cronus’s side and served as a leading commander of the Titans.

After the Olympians won, Zeus assigned Atlas a distinctive punishment: he had to stand at the western edge of the world and bear the heavens or celestial vault on his shoulders. This is different from the common modern image of Atlas carrying the Earth. Classical traditions generally describe him as supporting the sky.

Atlas also appears in the story of Heracles. During one of Heracles’ labours, Atlas obtained the golden apples of the Hesperides while Heracles temporarily carried the heavens. Atlas then tried to leave Heracles with the burden, but Heracles tricked him into taking it back. The word “atlas” later became associated with map collections, partly through Renaissance cartography.