The US President has had dinner with his relatives in Kenya as he started his "personal" visit to the country where his father was born.
It is the first time Barack Obama has been to the East African nation since becoming President, and many Kenyans view the trip as a kind of homecoming for him.
He was embraced on the tarmac on Friday at Kenyatta International Airport by his half-sister, Auma Obama.
He then went to his hotel in Nairobi for the dinner with around three dozen members of his extended family, including his step-grandmother, Mama Sarah.
Mr Obama said it was an emotional visit for him as he opened a business summit in Nairobi on Saturday.
"This is personal for me," he said.
"There's a reason why my name is Barack Hussein Obama.
"My father came from these parts, I have family and relatives here."
Announcing $1bn in new US investment at the Global Entrepreneurship Summit, he also heralded the continent as "on the move".
"Africa is one of the fastest growing regions of the world," he said.
"People are being lifted out of poverty."
Many of his official duties during the weekend visit are focused on boosting business and security ties with Kenya.
At a joint news conference with Kenyan President Uhuru Kenyatta, Mr Obama said Somalia's al Shabaab terror group had been "weakened".
"We have systematically reduced the territory that al Shabaab controls," he said.
"We have been able to decrease their effective control within Somalia and have weakened those networks operating here in East Africa.
"That doesn't mean the problem is solved.
"We can degrade significantly the capacity of the terrorist organisations, but they can still do damage."
Kenya has been working closely with American security agencies to combat the al Qaeda-linked extremists.
The group has been behind a number of fatal attacks in Kenya, including the 2013 Westgate mall killings.
Earlier in the day, Mr Obama laid a wreath at Memorial Park in Nairobi in memory of those killed in the 1998 US embassy bombing - an attack claimed by al Qaeda.
Mr Obama will later dine with Mr Kenyatta, who was indicted by the International Criminal Court for crimes against humanity.
Those charges were dropped in March, but the case prevented Mr Obama from going to Kenya.
Activists have raised concerns in a letter to Mr Obama about his trip to East Africa because of alleged human rights violations.
US National Security Adviser Susan Rice said the US President would not hesitate to raise such concerns on the trip.
Mr Obama last visited Kenya while serving as a US senator in 2006. This trip he is not expected to visit the community in western Kenya where his father was born and is buried.
Next he is heading to Ethiopia - he is the first sitting US president to visit either country.
In the Ethiopian capital Addis Ababa, Mr Obama will become the first US president to address the African Union on Tuesday before heading back to Washington.
The US President's critics say he has done less for Africa than his predecessor, George W Bush, whose AIDS relief programme made him a hero on the continent.
But Mr Obama's advisers point to his own initiatives on electricity, agriculture and trade.
The US President wrote about his Kenyan roots in his best-selling 1995 autobiography Dreams From My Father.
Debunked "birther" conspiracy theories once held he was actually born there, and ineligible to be US President.
Mr Obama showed his Hawaii birth certificate in the White House briefing room in 2011.