I want to preface this by saying that I personally don't see Nelson Mandela as a terrorist.
I'm referring more to the perception of him. Margaret Thatcher called him a terrorist, and Apartheid South Africa was a Western ally throughout the Cold War. So when and how did he begin to be viewed (in the West) as this heroic leader like MLK.
Also, I feel like his image was heavily sanitized; he supported Castro and opposed Israel, but Obama gave a speech at his funeral. How did this happen?
Much more can be said, but Why is Nelson Mandela so revered? Wasn't he a terrorist? written by u/khosikulu talks about the terrorist designation and some the changes to his international perception. This brief answer to What was Nelson Mandela's opinion on "Israel and the apartheid analogy"? written by u/ghostofherzl talks about his comments (or lack thereof) on Israel.
edit: fixed funky formating