"All of Manhattan was covered with festive decorations, and people of all races saluted their hero, Mandela," he recalls.

Since then Li has paid special attention to the freedom fighter, and in 2012 he was offered the opportunity to paint him.

A Chinese entrepreneur in South Africa invited him to paint a portrait of Mandela as a gift to the South African government. Li happily agreed.

He went to Johannesburg in early 2013, visiting the Apartheid Museum and meeting Mandla Mandela, the grandson of Nelson Mandela. During the 10-day visit, Li tried his best to collect information about Mandela. At the city square, he took lots of photos of local people so he could include them in his painting.

"We had had the chance to visit Mandela himself but we were advised not to do so, considering the old man's poor health," he says, adding that the actual image of Mandela was not that important to the painting.

"His image is well-known to the world. The key is to show his spirit."

But how to extract the essence of Mandela's tumultuous 95 years and put it on a huge painting? Li chose to present four decisive eras in that life: the prisoner, the president, the peacemaker and the funeral.