1947 A year before President Truman desegregated the military, Jackie Robinson debuts for the Dodgers becoming the first black player to participate in a major league game this century. In front of 25,623 Ebbets Field fans, the 28-year old first baseman is hitless in three at-bats, but scores a run in the 5-3 Opening Day victory over the Braves.
Jackie Robinson (though we should call him Jack: his real name, not the nickname that helped make him less threatening and more palatable to white audiences) is clearly a key figure in baseball, and American, history. After Babe Ruth, he is probably the most written-about figure in baseball history (the Black Sox scandal comes in third, I believe). If you want a great recent book about him, check out Opening Day by Jonathan Eig, which looks at the whole first season in real depth.
But the barrier set up in the early 1880s against African-American players was not the only race issue in the game. Way back in
1921 At Crosley Field, Pirates right-hander Chief Yellow Horse makes his major league debut against the Reds. The Pittsburgh hurler, a member of a North American Plains Indian tribe called the Pawnees, is believed by many baseball historians to be the first full-blooded American Indian to play in the big leagues.
Note the precision of "full-blooded" here: many major league players earlier had been Native American, just not full-blooded: the first being Louis Sockalexis—after whom the Cleveland Indians are named—Jim Thorpe, Zach Wheat, Chief Bender. Also note that how many Native Americans who played in organized baseball up to a certain date were inevitably nicknamed "Chief," just as German players were "Heinie" and deaf players "Dummy." Our national game is far from immune to our national habit of prejudice. But the "Heinie" bit is a great trivia question answer: who was the third baseman for most of the years the Tinker-to-Evers-to-Chance double-play combination? Harry "Heinie" Steinfedlt.
But for some sheer nickname poetry, dig this list of Hall of Famers and their monikers.