A spokesman for the Nelson Mandela Foundation confirmed Zulu was attempting to reach the summit with his wife Letshego when he encountered breathing problems.
"Details are sketchy. What we do know is that Gugu experienced problems breathing. The medical team supporting the trek put him on a drip and they descended the mountain with him. We are informed that the medical teams tried everything possible to save his life," they said in a statement.
The Foundation's CEO Sello Hatang said in the statement: "I am devastated. I recruited him to climb Kilimanjaro. The last thing he said to me at the airport before he left last week was that he wanted to speak about doing other Mandela Day projects. I feel a huge sense of loss."