At work it can be the developer who is pissed off the most about the code quality causing development pain or just naive enough to believe they might be rewarded if they care about the code.
In open source it is the pet project owner that often wants to see the project succeed.
It all comes down to who cares the most.
If you care you lay down industry best practices as the fundamentals, you tend the garden of knowledge and encourage pride in making your code the best. You mentor junior devs and put gates around your code to protect it. Fill your seats with developers who are willing to learn, challenge one another to greatness and when you find a hero, don't let them commit again until they have mentored two devs to take on the mantel.