President Obama arrives in Kenya on Friday, marking his fourth trip to sub-Saharan Africa since taking office.

His time in Kenya, his father's homeland, and then Ethiopia will mark the first visits to those countries by a sitting U.S. president.

Here is a brief look at key moments from some of Obama's previous trips, first as a senator in 2006 and then as president beginning in 2009:

South Africa, 2006:

Then-Sen. Barack Obama looks through the prison bars of former South African President Nelson Mandela's cell on Robben Island in Cape Town on Aug. 20, 2006.

Kenya, 2006:

Obama greets his step-grandmother, Sarah Obama, in Siaya, Kisumu, on Aug. 26, 2006.

Ghana, 2009:

President Obama delivers remarks to Parliament at the Accra International Conference Center in Ghana on July 11, 2009.

Senegal, 2013:

Obama looks out of the "Door of No Return" at the slave house on Goree Island, in Dakar on June 27, 2013.

South Africa, 2013:

Obama and British Prime Minister David Cameron pose for a picture with Denmark Prime Minister Helle Thorning Schmidt, next to Michelle Obama, during the memorial service for former South African president Nelson Mandela at FNB Stadium in Johannesburg on Dec. 10, 2013.

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