In the Harry Potter books, the spell that disarms an opponent is Expelliarmus.
Expelliarmus is a charm that typically forces an opponent to release a wand or other held object. Harry learns and uses it repeatedly, making the spell closely associated with his approach to magical dueling. Rather than immediately causing serious injury, it can give a wizard control of a confrontation by removing the other person’s weapon.
The spell becomes particularly significant when Harry uses it in public and during major conflicts. Its repeated appearance helps establish Harry’s preference for defensive or nonlethal magic, although the charm’s effectiveness depends on the caster and circumstances.
Expelliarmus is sometimes confused with Stupefy, which is the Stunning Spell, or Protego, which creates a magical shield. Riddikulus has a different purpose: it helps a person confront a Boggart by transforming its frightening form into something humorous.