Hackman and co-author Daniel Lenihan had been scheduled for a two-hour book signing, but the response was so large they stretched it to four hours, the Champaign, (Ill.) News-Gazette reported Sunday.
"I've been to book signings before," Hackman said. "I was worried no one would show up."
Hackman said he and his co-author write separately, then meet to discuss what they've written.
"We get together once or twice a week over coffee or drinks and critique each other," Hackman said. "I don't think we could write together. For one thing, Daniel uses a computer and I write long hand, but somehow we manage to thrash our way through it all."
Hackman said he hasn't worked as an actor for a year. "I'm getting to an age when acting is very tiring," he said. "I'm happy writing and painting."