The number one book I see recommended to people getting into the HA lore is 'Under and Alone' by William Queen. It's by an ATF agent who spent years undercover, so it cuts through a lot of the romanticized junk. Reading it gave me this constant low-grade anxiety for the guy, like you're in the room with him while he's trying not to slip up. That said, it's very much a law enforcement perspective.
For a more inside, if bitterly critical, view, Sonny Barger's autobiography 'Hell's Angel' is unavoidable. You have to read it with a huge grain of salt because he's myth-making the whole time, but the details about the early days, the runs, the politics—it's foundational. His voice is so distinct, arrogant and defiant, that the book itself feels like a performance.
If you want something that reads like fiction but is meticulously reported, 'The Electric Kool-Aid Acid Test' by Tom Wolfe isn't strictly about them, but the Merry Pranksters' interactions with the Oakland chapter are a wild snapshot of that cultural collision. It's less about club structure and more about a vibe, a really specific moment when outlaw bikers were part of a bigger, weirder American story.