Nelson Mandela spent 27 years in prison and emerged without bitterness

Nelson Mandela was imprisoned in 1964 for sabotage against the apartheid government, spending 18 years on Robben Island breaking rocks in a limestone quarry. Rather than breeding resentment, he used his time to study law, learn Afrikaans, and develop the political philosophy that would shape post-apartheid South Africa. Released in 1990 at age 71, he pursued reconciliation over retribution, becoming South Africa's first democratically elected president in 1994. 'I knew that if I didn't leave my bitterness and hatred behind,' he later said, 'I would still be in prison.'

Source: Mandela, Long Walk to Freedom (1994)