Ask HN: Have you seen a mediocre, stagnant developer become a “rockstar”?

If it's a programmer that started out okay but then stagnated for a long while, and then through some visible changes has recovered from stagnation and built a good reputation whose experience meet the expectations.

Whether it's a co-worker you've had over the years or a peer that you've talked to and seen grown pretty well in experience, jobs, and reputation. What was your experience with them like? How did they improve?