When we think of Latin America, we think of a sprawling quilt of Hispanic cultures sewn in Spain. What we know much less about is the huge African-American population that has been in the region since the Spanish first brought African slaves there. premiers

“Upward of 120 million people of African descent live in Latin America today,’’ says Harvard professor Henry Louis Gates Jr., who, even though he is a scholar of African-American history, says he was staggered by the number when he first learned of it.

Gates is the ubiquitous face and voice on PBS of the African-American experience whose previous documentaries have focused on the lives of blacks in Africa and this country

In his new four-part series called “Black in Latin America,’’ which first airs Tuesday on WGBH 2 at 8 p.m., he opens our eyes to the huge, complicated profile of blacks in that region and also provides us the proper context in which we should view American slavery.

“We have our African-American exceptionalism,’’ says Gates. “We think slavery was all about us. In fact, 11.2 million Africans got off boats in the New World. Only 450,000 came to the US. All the rest came to areas south of Miami. The real African-American experience unfolded in the Caribbean and Latin America.’’

“Black in Latin America’’ is the final piece of the trilogy that began in 1999 with Gates’s series “Wonders of the African World.’’ Then came “America Beyond the Color Line’’ in 2004 on the black American experience in this country, and now his latest.

As with the earlier series, he wrote and presents this one, traveling to six countries for the stories: the Dominican Republic, Haiti, Cuba, Brazil, Mexico, and Peru. In each country, Gates talks to its best historians and cultural observers about past and present roles that African blacks have played. These are uniformly fascinating conversations.

So, too, are those he has with people on the street. He asks one group of young men in Brazil what race they consider themselves. There was no consensus.

In the first episode, Gates explores the tortured divide between the Dominican Republic and Haiti, two sides of the island once called Hispaniola. The Dominican culture is Spanish, and successive governments there have despised and brutalized the African blacks who dominate Haiti.

Dominican dictator Rafael Trujillo, whose bloody rule lasted for three decades, did all he could to separate Dominicans from Haitians, whom he considered inferior people. In 1937, Dominican soldiers massacred thousands of Haitians, creating an irreparable gulf.