I recommend you to the book „Ethical Leadership in Organizations : Concepts and Implementation“ by Bernhard Bachmann, Springer 2017. In his research, Bachmann comes to the conclusion, that companies for too long have depended on codes, on process orientation, on rule books and on implementing CSR as part of corporate governance, without changing the leadership realities, and the operational governance. According to him leadership, culture and change need to be aligned; these forces and activities need to overlap each other.
Many traits have been used to define effective leaders. However, I believe integrity which includes honesty and truthfulness; courage, consistency and among all others leading by example to be the most important. Icons and Idiots by Bob Lutz is a book that discusses a number of leaders mostly from industry and their various leadership styles that you may find of interest.