What hundred-handed giants helped Zeus overthrow the Titans?

The hundred-handed giants who helped Zeus overthrow the Titans were the Hecatoncheires.

The Hecatoncheires were three brothers—Cottus, Briareus, and Gyges—born to Uranus, the sky, and Gaia, the earth. Each possessed one hundred arms and fifty heads, making them among the most formidable beings in Greek succession mythology. Their collective name comes from Greek words meaning “hundred” and “hand” or “arm.”

Uranus imprisoned them, and later traditions also place them in Tartarus. During the Titanomachy, the war between Zeus and the Titans, Zeus released them and restored their strength with nectar and ambrosia. They hurled enormous rocks at the Titans, helping secure the Olympians’ victory. In some accounts they later guarded the defeated Titans in Tartarus.

They are often confused with the Cyclopes, who were also imprisoned and aided Zeus, but Cyclopes were one-eyed giants who forged his thunderbolts. The Titans were Zeus’s opponents, while the Gigantes belonged to a later generation of earth-born adversaries.