"He loves it," Bizos said. "If it were not for his doctors and senior members of his family, protective as they are, he would accept every invitation.
"The whole world wants to see him and he would willingly do it. He is a humanist down to the core."
In his later years, surrounded by devoted friends and family, Mandela has reconciled with his second wife Winnie, as well as his former foes. Three daughters -- Makaziwe with Mase and Zindziswa and Zenani with Madikizela-Mandela -- are still living.
"He is too generous and forgiving of people," Bizos said. "I can't bring myself to be kind to some of the people who were so cruel to him by implication and others who were detained without trials, had their relatives tortured or killed. He says it's important for the future."
Though today's anniversary is not a national holiday, Mandela's birthday has been an annual cause for celebration across South Africa and on his 90th, two runners holding national flags circled Robben Island, Johannesburg children brought cakes to Mandela's foundation offices and the ANC headquarters unveiled giant banners with his image.
But that iconic image has been "somewhat twisted by time," Mandela researcher Sanders said. "He is really a human being with a lot of faults. He was always incredibly insistent that we not paint him as a saint.
"He's not a mythical figure," he said. "And I know that sounds odd, but one byproduct of racism is to create icons that are incredibly good or evil. He gets that 10 times over."
Although not particularly intellectual, Mandela was a "politician to his fingertips," Sanders said.
"He had enormous energy poured into him -- black liberation and white reconciliation or the global need for some progressive figure of good," he said. "And he didn't want to let them down."
Mandela's imprisonment, especially, shaped his view of the world and his ability to be a reconciler, Sanders said. "The only way you can survive is to go by a set of parameters of what is given," he said.
Still, Mandela gives South Africa, which continues to be challenged by poverty, the highest rate of AIDS in the world and lingering racism, the opportunity to "feel good about themselves," he said.
"He was a contested figure and he urges contestation of who is," Sanders said. "He tried to use his influence and power and the experience that gave him to positive ends and he was marvelous at that."
And to his fellow South Africans, many of whom fled to the United States during the apartheid years, Mandela is a symbol of determination.
"The most fascinating thing about him is he kept his eye on the prize," said Dr. Wulf Utian, consultant in women's health to the Cleveland Clinic, who left South Africa 33 years ago.
"He was focused and never allowed hate or bitterness or political factions or even pressure from different groups within the ANC to take away his clear thinking toward a multi-racial country."
ABC's information specialist Nicholas Tucker contributed to this report.