According to an account told by Shari, an angry Cu Chullain used the Gae Bolga to strike the Stone of Destiny in half when it would not accept his friend, Lugaid Red-Stripe, as High King of Ireland. ("Rock & Roll") Centuries later, when the Avalon World Tour travellers came to Ireland, Cu Chullain, in his reincarnated form of Rory Dugan, discovered Gae Bolga inside Cairn na Chullain. With Bronx's help, he defeated the Banshee with the spear as he had done once before in his career as the legendary Hero of Ulster. ("The Hound of Ulster")
The Gae Bolga looks like a rod of brilliant light, and returns to Cu Chullain's hand after it's thrown. When not in use, it reverts to the form of an ordinary stick.
Real World Background
In Irish legend, the Gae Bolga was a magical spear which Cu Chullain received from his tutor in arms, the warrior woman Scathach. When hurled at an enemy, it struck him in the stomach, and opened up thirty barbs to increase its damage. The "Spear of Light" appearance of the Gae Bolga in Gargoyles may have been inspired by the fact that, in the legends, Cu Chullain's father was Lugh, the god of light.