Crowning achievement phrase
The greatest, the most notable, or outstanding achievement or moment of someone's life/career.
The crowning achievement of Albert Einstein was the general theory of relativity.
As a recent graduate of ABC University, my crowning achievement was graduating in the top 3% of my school, with a GPA of 3.8.
The crowning achievement in her career achievement was being the youngest person ever awarded a sales management position at her current company.
The origin of this phrase is not clear.