WASHINGTON — When President Obama lands in Yangon on Monday, he will be the first sitting American president to visit the country now known as Myanmar. But he will not be the first Obama to visit.

The president’s Kenyan grandfather, Hussein Onyango Obama, spent part of World War II in what was then called Burma as a cook for a British Army captain. Although details are sometimes debated, the elder Mr. Obama’s Asian experience proved formative just as his grandson’s time growing up in Indonesia did decades later.

“His roots go through Burma,” said Timothy Parsons, an African history professor at Washington University in St. Louis who wrote a book on the colonial East African military. “It is kind of an odd intersection of his life. It’s like the three corners of the triangle come together — America, East Africa and Southeast Asia.”...