They attack by butting with their large horns. They add +6 to damage inflicted when they charge, and they attack as +16 hit dice monsters.
Thrym is both leader and deity of the frost giants.
That's from the 1980 Deities & Demigods published by TSR.
This represents the hazards of being a pack-rat and having a five-year-old daughter who can read: it's the nearest book on the floor. Below is what was once her favourite goddess, although she has fortunately forgotten what page it's on and is now stuck with Japanese mythos: