"Professor Ajulu is a renowned internationalist and academic, he has contributed immensely to not only academia but also to the struggle for liberation in his own native Kenya and South Africa. His passing is a great loss to his family, South Africa and indeed the continent," Zuma said in a statement on Wednesday.
"On behalf of government and all South Africans, we wish to extend our heartfelt condolences to Minister Sisulu as well as Ajulu and Sisulu families. Our prayers and thoughts are with them during this difficult period. May his soul rest in peace."
Sisulu is the daughter of struggle stalwarts Walter and Albertina Sisulu.
According to a Kenyan Daily Nation story back in 2009, Ajulu was one of the academics who fled the country at the height of the Daniel Arap Moi repression targeting independent thinkers and perceived dissidents in the early 1980s. He told the paper at the time that he was not surprised that his wife had then been appointed as defence minister because she "was a fairly senior minister already".
During the interview, he revealed that while visiting his home country he preferred to stay "in his rural home in Bondo because it is cheaper".
He was a man who reportedly never forgot "his Kenyan roots".
The couple met in exile and reportedly married in 1996.