Kenneth Kaunda, Zambia’s founding president and liberation hero, has died at a military hospital in the capital, Lusaka, where he was being treated for pneumonia. He was 97.

Kaunda ruled Zambia from 1964, when the Southern African nation won its independence from Britain, until 1991, and afterwards became one of the most committed activists against HIV/AIDS in Africa.

"I am sad to inform [members] we have lost Mzee [the old man]. Let’s pray for him,” Kaunda’s son Kambarage said on the late president’s Facebook page on Thursday.

Authorities declared 21 days of mourning for the liberation hero.

"On behalf of the entire nation and on my own behalf, I pray that the entire Kaunda family is comforted as we mourn our first president and true African icon,” President Edgar Lungu said in a message on his Facebook page.

The former president – affectionately known as KK – had been feeling unwell and had been admitted to the Maina Soko Medical Centre in Lusaka on Monday.

Although Zambia’s copper-based economy fared badly under his long stewardship, Kaunda will be remembered more for his role as an anti-colonial fighter who stood up to white minority rule in Southern African countries such as Angola, Mozambique, Namibia, South Africa and Rhodesia, now Zimbabwe.

The youngest of eight children, Kaunda lost his father when he was eight years old. His mother was a teacher – a rare profession for Zambian women in those days.

He started his political career as the organising secretary of the Northern Rhodesian African National Congress (NRANC) in the Northern Province of Zambia.

But in 1958, he broke from the NRANC to form the Zambian African National Congress (ZANC). The colonial authorities banned it a year later, and Kaunda was imprisoned in Lusaka for nine months.

ZANC became the United Party for National Development (UNIP) in 1959.

The following year, Kaunda was released from prison and elected president of the nationalist, left-of-centre UNIP. He then started organising civil disobedience known as the Cha-cha-cha campaign.

It was the philosophy of Mahatma Gandhi that made Kaunda committed to non-violent principles.

Kaunda was not ashamed to weep in public and had a unique speaking style, emphasising key thoughts by repeating whole sentences, his trademark white handkerchief in his left hand.

He espoused an ideology of "humanism” mixing Christian ethics, traditional African values and socialistic principles.

Using his rhetorical skills to appeal to the public, Kaunda won independence for his nation without resorting to violence in 1964. As UNIP president, he ruled Zambia for 27 years.