When Barack Obama visited Kenya for the first time nearly 30 years ago, he was astonished that an airport worker recognized his last name.

It was a striking experience for a young man - and future US president - struggling to understand how a country he had never seen and a Kenyan family he barely knew had shaped his identity.

"My name belonged and so I belonged, drawn into a web of relationships, alliances and grudges I did not yet understand," Obama wrote in his memoir, Dreams From My Father, about the airport encounter.