Benjamin Franklin's fertile mind constantly spun off inventive and useful ideas. His lightning rod saved buildings and lives. His energy-saving improvement of the wood-burning fireplace kept families warm and forests from being leveled.

His lending library extended literacy to those who couldn't afford books. His map of the Gulf Stream made travel faster and commerce more efficient. But Franklin's ingenuity showed most clearly in his invention, or rather recurrent reinvention, of himself.

In the course of his life, Franklin devised dozens of authorial personas in print, which allowed him to challenge authority, identify folly and promote human progress with an unsparing vigor he never could have achieved under his own name. Franklin created his first alter ego when he was in his teens: a middle-aged widow named Silence Dogood. Mrs. Dogood allowed Franklin to evade an embargo against publication imposed by his jealous elder brother James, a printer to whom Ben was apprenticed. James had a newspaper and sought contributors, but he refused Ben's submissions as corrosive of the master-apprentice relationship.

So Ben disguised his handwriting and surreptitiously slipped letters from Mrs. Dogood under the door of the print shop. Franklin's account of her life delighted readers while underscoring the difficulties facing widows and women of the day. Franklin's most famous alter ego was Richard Saunders, an astronomer and a polymath who annually published Poor Richard's Almanack.

The almanac provided information on holidays, solstices, phases of the moon and the like. What made it special were the squibs of advice and humor that filled otherwise blank spots on the pages. Franklin retired Saunders after going into politics—a move that inspired him to create additional personas.