I've researched about Nelson Mandela.
1) He was tolerant. Imagine yourself doomed in prison for 27 years. But most importantly, he had a vision, to end the apartheid policy, not only in South Africa, but elsewhere too. Since he got into politics very early, he gained some tough experience or better say it was a 'long walk to freedom'.
He was also a lawyer. Legal reform is the prime objective for a long lasting political stability.
I recommend you analyse his leadership qualities in comparision to other leaders like Lincoln.
2) A good leader is tolerant, brave, and bold.