Integrity

The MMM has on more than one occasion focused on the importance of integrity.  Reputations and relationships rise and fall based on integrity or the lack of it.  I have tried to live a life where integrity is not only important to me, but is also clearly visible to others.  I think it is one of the greatest keys to leadership, not to mention one of the finest qualities we can pass on to our children.

In looking for people to hire, you look for three qualities:
integrity, intelligence, and energy. And if they don't have
the first, the other two will kill you.
--Warren Buffet

Warren Buffet sums it up nicely, but I would not limit it to people I hire.  I look for integrity in people that I develop relationships with in all aspects of my life.  So many great qualities are found where there is a solid base of integrity.