What do we call the heavy horse soldiers of the Middle Ages?

The story behind the answer

In medieval Europe, elite mounted warriors wore mail and later plate armor, rode powerful destriers, and delivered shock charges with couched lances under a chivalric code. Their status was bound to feudalism: in exchange for land (fiefs), they owed mounted service to their lords. Innovations like the high-backed saddle and stirrup let them transfer immense force on impact, making them dominant from the 11th to 14th centuries.

By contrast, “cavalry” is a broad category; “men-at-arms” were professional soldiers who might fight mounted or on foot; and “cataphracts” refer to earlier Greco-Roman/Byzantine and Persian heavy horsemen. Pike formations, longbows, and gunpowder gradually eroded the battlefield supremacy of knightly cavalry.