“You can’t make this up,” Ken Burns says more than once as we discuss the life of Muhammad Ali, the subject of his new eponymous 4-part docuseries, which you can now stream on PBS’ site. As with projects centered around Jackie Robinson and The Central Park Five, the Ali series is co-directed by Burns’ daughter Sarah Burns and her husband David McMahon. It’s also exhaustive, with Burns estimating that they accumulated approximately 50 times the 8 hours of material that they wound up using in the finished product. And that’s the great appeal of yet another doc on a man who is arguably the 20th century’s most fascinating, outspoken, and documented person: the promise that we might better understand his journey and the waypoints of his life that so inform our memory of him as a hero, as a fighter in and out of the ring. We spoke with Burns about that pursuit, the basis of how and why he chooses his projects, his relationship with PBS, and whether he might go back to expand on one of his most famous past works.