Final answer:
While the top grossing documentary director is not specified, Ken Burns is a prominent documentarian known for his comprehensive American history films.
Step-by-step explanation:
The director of the top grossing documentary of all time in the United States is not specifically mentioned in your provided text or widely known as a single individual, as documentary revenues can fluctuate over time and by specific metrics. However, a notable figure in the field of American history film documentaries is Ken Burns. He has created a significant number of documentaries, including The Civil War (1990), The Vietnam War (2017), Jackie Robinson (2016), and Country Music (2019). These films are known for their comprehensive coverage of the American experience through a combination of archival footage, expert interviews, and narrative storytelling, often featuring well-known narrators.