What is a leader’s most important contribution to group culture?

A leader cannot change group culture unless they have the vision to hire individuals that have their desired culture. When the majority of the individuals have the desired culture, they will metaphorically surround the individuals without the desired culture and those other individuals will either change their mindset or will eject themselves. So, in summary, leaders must have the vision to hire those with the right culture and only then will the leaders contribute to group culture.