Cinderella
A person or team that unexpectedly rises from underdog to winner.
A Cinderella is someone who achieves unexpected success or recognition after being overlooked, mistreated, or underestimated. The word comes from the famous fairy tale about a young woman forced to work as a servant by her cruel stepfamily, who transforms into a princess for one magical night and eventually marries the prince.
When people use Cinderella outside the fairy tale, they're usually describing a dramatic rise from obscurity to triumph. A Cinderella story in sports is when an unknown team defeats all the favorites and wins the championship. A Cinderella candidate is a politician nobody expected to win who suddenly captures everyone's attention. The word captures that thrilling feeling of an underdog finally getting their moment to shine.