Final answer:
Sidney Poitier is the pioneering black actor who challenged stereotypes by playing a doctor, businessman, and police detective, notably recognized as the first African American to win an Academy Award for Best Actor.
Step-by-step explanation:
The black actor who broke down stereotypes by taking on the roles of a doctor, businessman, and police detective is Sidney Poitier. Poitier was an iconic figure in Hollywood and a trailblazing African American actor who won an Academy Award for Best Actor.
His remarkable performances are evidenced in groundbreaking films such as Guess Who's Coming to Dinner and In the Heat of the Night, which dealt with themes of racial intolerance.
Furthermore, Poitier's work paved the way for future generations of African American actors and had a significant impact on the portrayal of Black characters in cinema.