Hammer Bros. are recurring enemy characters in the Super Mario series, usually appearing as armored turtle-like Koopas that attack by throwing hammers at Mario and Luigi. They are typically encountered in groups or as tougher mid-level foes, often guarding platforms, castles, or other dangerous areas. Their role is to create a more challenging obstacle than standard enemies, forcing players to time jumps carefully and avoid projectile attacks. They are one of the most recognizable enemy types in the franchise.