Asterius was an elderly male Minotaur that lived during the time of the Narnian Revolution. He lived in hiding in the Shuddering Woods, along with the other Old Narnians, and aided Caspian X and thePevensies against King Miraz and his Telmarine army. Like the other Old Narnians, he longed to see their homeland returned to its former glory.

He was obviously born in hiding, during the years before the War of Deliverance, though no one knows exactly when he was born.

He was present at the meeting at the Dancing Lawn, and was one of the Narnians who were willing to blame Caspian for what the Telmarines had taken from them, however he soon accepted Caspian as his king.

When the Pevensies tracked down the Narnians, Lucy Pevensie, having mistaken Asterius's growls as those of Aslan, started to approach him until Peter stopped her. Since Minotaurs were originally allies of Jadis, Peter didn't think they had changed their ways. He was about to attack Asterius with his sword, but was stopped by Caspian. Caspian and Peter dueled until they were stopped by Lucy. This led up to the Pevensies and Trumpkin joining forces with Caspian and the Narnians.

Asterius moved to Aslan's How with the rest of the Narnians and became the de facto general of the army. He then later took part in the Telmarine Castle Night Raid.

When they first reached the castle, he shushed a Telmarine while Nikabrik snuck up behind him, and knocked him out.

After that, Asterius was one of those who led the charge into the castle, knocked down a gate, and then rammed a Telmarine with his horns.

Near the end of the battle, the gate started to close, threatening to trap the Narnians within the castle courtyard, where the Telmarines were waiting to shoot them down with their crossbows. When he saw this, Asterius valiantly ran below and attempted to hold the gate up all by himself, but he was then shot to death with arrows from a crossbow by Miraz and many Telmarine soldiers, but not before helping most of the Narnians escape.