I am one of the titans slain by Hercules?

You are likely referring to the Titan Atlas, who was famously vanquished by Hercules during his Twelve Labors. Hercules tricked Atlas into taking back the weight of the heavens temporarily while he retrieved the golden Apples from the Garden of the Hesperides. In some accounts, Atlas is depicted as being burdened by the weight of the sky, contrasting with Hercules' strength and cunning in overcoming him.