This is from USA Today:
"Mandela veered from non-violence as a method for change and argued for setting up a military wing of the ANC and violent tactics to bring down apartheid...In 1961, Mandela became the leader of the ANC's armed wing in which he oversaw bomb attacks against government buildings. He was designated a terrorist by the white government and arrested in 1962. In June 1964, he was sentenced along with seven others to life in prison for plotting to overthrow the government through hundreds of acts of sabotage...
He spent 18 years of his imprisonment at Robben Island Prison off Cape Town, where the harsh conditions included laboring in a lime quarry. During that time, he became the focus of an international campaign for release led by his lifelong friend and law partner, Oliver Tambo, and Mandela's wife, Winnie, whom he married in 1958 after his first marriage to Evelyn Mase ended in 1957.
In the 1980s, the ANC under Tambo ramped up bombing attacks to include civilian targets. In one of the worst examples, an ANC car bomb exploded in downtown Pretoria in May 1983, killing 19 people.
In an attempt to calm the violence, President P.W. Botha offered in 1985 to free Mandela if he would renounce violence as a tool for change. Mandela refused."
Mandela was a murdering terrorist. That doesn't make him a hero. Neither does his spending 18 years in prison. He could have followed in the footsteps of Mahatma Gandhi advocating nonviolent rebellion, and been a truly great and heroic figure, but instead he became a leader in a terrorist organization directing bombings against the government and innocent people, and refused to renounce violence even while in prison. Mandela was a terrorist dirtbag.