Atlas is said to be holding the entire weight of the sky on his shoulders as a punishment for his participation in the Titanomachy. He is probably the most well known of the titans.
After losing the Titanomachy, Zeus punished him by forcing him to carry the sky on his shoulders. Later, during Herakles' Twelve Labors (specifically the task of retrieving the golden apples), Atlas gave Herakles the burden of the sky as he agreed to fetch the golden apples from the Garden of the Hesperides, who were his daughters. Atlas planned never to take upon himself the sky again; but after Herakles learned this, he asked if Atlas would at least help him adjust the weight of the sky upon his shoulders. Atlas agreed, but in doing so, took the sky back from Herakles, who immediately fled.