Barrels are one of the two weapons that Donkey Kong used against Mario in Donkey Kong (arcade game). Mario could jump over them or smash them with his hammer. Since then, barrels have appeared in many other Donkey Kong and Mario games. In the Donkey Kong series, many barrels can be picked up and used to attack Kremlings and other enemies.
Some barrels are containers. Some containing bananas, coins, and balloons.
Barrels also appear as items in Super Smash Bros., Super Smash Bros. Melee, and probably Super Smash Bros. Brawl, where they contain four items and can roll along inclines. They also sometimes explode on contact.