Jackie Robinson is the first black player in modern (post-1900) baseball. Young Jackie moved from Cairo, Georgia to Pasadena, CA, where he grew up and attended UCLA. During World War II he made lieutenant. Promoter Branch Rickie selected Jackie for the toughest assignment of his life, integrating professional baseball, a task at which Jackie proved worthy. He silenced his critics, frequently turning them into supporters (like The Sporting News).
For more on the Ebbet's Field hero, see Jackie Robinson bio
The first black player in baseball was Moses "Fleet" Fleetwood, who played before rules regarding segregation of black and white players were established. In fact, they were established because powerful white ballplayers objected to playing with Fleetwood.