The Paladin is the Diablo II class associated with the shield-based Smite attack.
Smite is a Paladin skill that strikes an enemy with the character's shield. Unlike an ordinary weapon attack, it has distinctive mechanics, including the ability to stun its target. The Paladin's skill trees also include Combat Skills, Offensive Auras, and Defensive Auras, giving the class a mix of direct attacks and party support.
The class was present in the original Diablo II and remained important in Lord of Destruction. Paladins became especially recognizable for builds combining powerful auras with shield attacks, including the well-known Hammerdin and Smiter archetypes.
The question identifies the class rather than a particular build. A Barbarian can use shields, and other classes can equip them too, but Smite is specifically a Paladin skill in Diablo II.