Strong corporate culture starts from the top with the co-founders. If the co-founders don’t emphasize corporate culture it’ll take on a life of its own, even more so than it already does. As the company grows, middle management will drive corporate culture if it isn’t pushed from the top, and the outcome can be fine but the only sustainable competitive advantage that’s completely controllable will be lost.
When a company is starting out it’s important for the co-founders to interview and approve every new hire. Only A players hire A players. As the company gets larger, around 100-200 employees, it becomes much more difficult for the co-founders to be involved in all the hiring. At this point designated Keepers of the Culture should already be trained and at least two should be in every hiring process — exclusively assessing corporate culture fit.
How do you train Keepers of the Culture? Easy, get them involved in the hiring process at an earlier stage in company growth and have them interview a significant number of potential hires and compare cultural fit with the notes from the co-founders. Only after the Keepers of the Culture and the co-founders opinion match 100% of the time are the Keepers of the Culture ready to carry the torch forward, and train future Keepers of the Culture.
What else? What are your thoughts on Keepers of the Culture?
David Cummings on Startups 
Thanks for pointing out the importance of culture. As an experienced entrepreneur and an educator, this is something I stress to my students and practice in my own business. Please check out my blog at http://www.benjaminjgoldman.com if you are interested in what I am thinking about regarding entrepreneurship.