Researching the life of Leonardo da Vinci left Walter Isaacson in a playful mood. "He's the most fun, joyous person I can imagine," says the best-selling biographer, whose "Leonardo da Vinci" comes out Oct. 17. "And that was the big surprise. I thought he was going to be this brooding genius."

Isaacson, 65, sees the da Vinci book as the culmination of his biographies about innovators that include works on Steve Jobs, Benjamin Franklin and Albert Einstein. Long fascinated by those who wedded logic and creativity, he says da Vinci left us with dazzling works of art and scientific breakthroughs and was also a model for a more joyous and spontaneous way of life. Isaacson spent extensive time with Jobs, but his book on da Vinci, who died in 1519, seems more personal.