Gerry Whelan was 23 years old and working in a stockbroking firm on Wall Street in 1980s New York when he changed his profession. He packed his bags, signed up with the Jesuits and flew 7,000 miles around the globe to Kenya, where he swapped stock options for street children.
Yesterday he welcomed the President, Mrs McAleese, to the school he helps run in a teeming slum on the edge of Nairobi. Many of the pupils at St Joseph the Worker once slept on the streets; an estimated 60,000 still do so today. "The problems are much bigger than what we can do," he said.
"There's a sense that what we do is of symbolic value."
Money is short, and Father Whelan is seeking funds through his alma mater, Gonzaga College in Ranelagh, Dublin. Business is in his blood. His father Michael was founder and chief executive of the now-defunct energy firm Aran Energy.
Yesterday, he celebrated his 42nd birthday party while waiting for President McAleese to arrive. "This is quite a present," he said.
There was also a birthday at St Austin's Holy Ghost mission, where Sister Miriam Madden was celebrating her 86th birthday. The Belfast woman came to Kenya in 1938 as one of the Carmelite pioneers.
She has no intention of returning home. "I'm going to leave my bones in Kenya."
The Holy Ghost Fathers were the first missionaries to arrive in Kenya in 1899; they were also the first people to plant the coffee seeds that are now one of the country's big export earners.
Their regional supervisor, Father Sean McGovern, was once known as "the camel man" among his peers for having single-handedly imported a new breed of camel into Kenya by plane from Pakistan in 1990.
When Father McGovern arrived in Kenya in 1965 there were 160 Holy Ghost Fathers, also known as Spiritans. Today there are just 25, but the number has remained constant thanks to a surge in African vocations.
"That's the way of the future," he said.
At the nearby St Mary's school, students from the Muslim, Catholic, Protestant and Jain faiths sketched some of the cornerstones of their beliefs before the president. "It's not a narrow, shove-it-down-your-throat mission," said principal Father Michael McMahon.
"But we do present the message of Christ and those who are interested can ask questions."
Later Mrs McAleese laid a wreath at the grave of Edel Quinn, the lay missionary who came to Kenya in 1938 to establish the League of Mary in East Africa.
Ms Quinn died in 1944 of tuberculosis; the President said she was a personal hero and had taken her name for the sacrament of confirmation in her honour.
The President is spending her final day in Africa today - she is due to visit a slum project and a rural mission hospital - before returning to Dublin tomorrow morning.