Nelson Mandela, circa 2000. (23379)

As Nelson Mandela lies ill in a South African hospital, the world celebrates his 95th birthday Thursday, honoring his legacy in various ways, including performing 67 minutes of community service.

School children in the nation will sing “Happy Birthday” to the revered statesman in unison. The day also marks 15 years since he married his wife, Graca Machel.

The United Nations declared July 18 as Mandela Day four years ago to honor his role in reconciling a country torn apart by apartheid. It started as a call to promote global peace and encourage community service.

His foundation is asking people to take part in at least 67 minutes of public service on his birthday, a reference to the number of years he devoted to public service.

While the world marks his birthday, the revered statesman is battling a lung ailment at a hospital in Pretoria.

President Jacob Zuma said Mandela, who has been hospitalized since June, is steadily improving.

“We are proud to call this international icon our own as South Africans and wish him good health,” Zuma said in a statement. “We thank all our people for supporting Madiba throughout the hospitalisation with undying love and compassion. We also thank all for responding to the call to give Madiba the biggest birthday celebration ever this year.”

South Africans affectionately refer to Mandela as Madiba, his clan name.

U.S. President Barack Obama, who visited with Mandela’s family in South Africa last month, paid tribute to his birthday.

“People everywhere have the opportunity to honor Madiba through individual and collective acts of service,” he said in a statement. “Through our own lives, by heeding his example, we can honor the man who showed his own people — and the world — the path to justice, equality, and freedom.”

The frail icon has not appeared in public for years, but still retains his popularity as the father of democracy for his fight against apartheid.

His defiance of white minority rule focused the world’s attention on apartheid, the legalized racial segregation enforced by the South African government until 1994.

His hospitalization has given his birthday a sentimental touch. The South African Embassy in the United States said this will be the biggest celebration since his 1990 birthday — the year he was freed from prison.

The festivities were not limited to South Africa. In the United States, the embassy said activities to mark his birthday are planned in 18 cities, including the nation’s capital.

The United Nations will also mark the day with an event in New York city featuring various speakers including former U.S. President Bill Clinton, whose presidency coincided with Mandela’s. Civil rights leader Rev. Jesse Jackson, singer and actor Harry Belafonte, and Andrew Mlangeni, 87, who was imprisoned with Mandela, will also be part of the celebration.

Mandela, a Nobel peace laureate, spent 27 years in prison for fighting against oppression of minorities in South Africa. He became the nation’s first black president in 1994, four years after he was freed from prison.

Faith Karimi | CNN