Bob LeVitus has written nearly 100 reference books on Apple technologies. He’s the author or coauthor of macOS For Dummies, iPad For Dummies, and iPhone For Dummies, among others.
Dwight Spivey probably wrote the rest of the For Dummies books on Apple products, including iPhone For Seniors For Dummies, iPad For Seniors For Dummies, and Apple Watch For Seniors For Dummies.