knight in shining armor
A rescuer or defender, as in What this political party needs is a knight in shining armor to change its tarnished image. This metaphoric expression alludes to a medieval knight. [Mid-1900s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.