Who is Nelson Mandela

I love the show America's Next Top Model by the former model Tyra Banks. I watched all cycles from one to six. I love the countries and sites they visited. I remember, one time, they visited the cell of Nelson Mandela when America's Next Top Model cycle four went to Cape Town, South Africa. I wondered, "Who is Nelson Mandela?" Please excuse my ignorance over the subject, but I don't have any clue who he is. My friend who is good in history told me that Nelson Mandela was the first ever president of South Africa.