While Atlas is a prominent figure in Greek mythology (known for holding up the sky), he doesn't feature in any of Rick Riordan's *Percy Jackson* books.
Perhaps you're thinking of another character who might remind you of Atlas. There are a couple of possibilities:
* The Titan who holds up the sky in *The Titan's Curse*: It's Cronus, who, in that book, briefly holds up the sky to save his children.
* The giant who holds up the sky in *The Battle of the Labyrinth*: It's the giant Makhai, who is tricked into doing so by Daedalus, a human architect.
Let me know if you have any other questions about the *Percy Jackson* series!