Every great leader had or has a great mentor. And every leader should sooner or later act as a mentor. Why? In mentoring and in teaching you as the mentor will also learn and develop. At the same time learning and growing will eventually enable your mentee to become a teacher and mentor herself.
Steve Jobs e.g. often asked his mentor Bill Campbell for advice whilst those who credit Jobs as a mentor include Facebook founder and CEO Mark Zuckerberg and Larry Page of Google. Since there is a contributing and receiving end in the mentoring process, I´m a big fan and user of this beautiful concept.