After graduation, Schulz’s shyness and insecurity rendered art school out of the question, so instead he took a correspondence course from Art Instruction Inc., the kind of place that used to advertise on the back of matchbooks. (He found the instruction so helpful that he eventually joined the faculty himself and years later went on the board.) In 1942 Schulz was drafted and, heartsick and terrified, left for boot camp only days after his mother had died. But he actually thrived in the Army and came back newly confident. He even began to go out with girls — though his idea of an appropriate dating present was a Bible. (All his life Schulz was the straightest of arrows: he didn’t smoke, swear or drink, on the grounds that neither did Jesus. The wine at Cana, the young Sparky used to claim, was nonalcoholic.)

In 1951, Schulz married Joyce Halverson, a 22-year-old divorcée with a young daughter from an ill-advised and short-lived marriage to a cowboy. He arranged to adopt the daughter, Meredith, and afterward always insisted she was his, even when the teenage Meredith began to poke around and ask nosy questions. To some degree it was probably a marriage of convenience on both sides, but for a while it was happy enough, and the Schulzes went on to have four children of their own. Sparky was an indifferent and often inattentive father and husband, though, because, self-absorbed and secretly harboring immense ambition, he was really married to his work. After a lot of rejections and false starts, he finally landed a weekly strip, called “Li’l Folks,” with the St. Paul Pioneer Press, and it was syndicated in 1950 by United Feature, which insisted that the title be changed to “Peanuts.” Schulz hated the name but went along, adding this to his ever-growing list of grudges.

Schulz had initially dreamed of an action strip but began drawing children because that’s what seemed to sell. The earliest strips hit what now seems the authentic Schulzian emotional tone — “Yes, sir! Good ol’ Charlie Brown. ... How I hate him!” — but it took a while for the drawing to evolve, for the heads to enlarge, the limbs to shrink.

“Peanuts” grew slowly at first; caught on hugely in the ’60s, when almost by accident it seemed to speak to everyone who was experiencing the generation gap; and then almost drowned in a licensing binge and flood of tchotchkes. Schulz said yes to everything, no matter how kitschy — toys, cards, books, sweatshirts — until even his fans began to complain he was selling out.

What saved “Peanuts,” Michaelis suggests, was the elevation of Snoopy into a main character in the late ’60s, and the way his boundless, almost surreal fantasy life frequently took over the strip, which at the same time was being pared down to a visual minimum: a scarf, a helmet, a doghouse indicated by just a few horizontal lines. Another thing that didn’t hurt was the gradual souring of the Schulz marriage. The family was living in Northern California by now, on a sort of private Disneyland with its own stables and miniature golf course and the ice rink (where Schulz like to hold court in the Warm Puppy snack bar) nearby. Despite his success, Schulz was prickly, lonely, depressed and increasingly subject to panic attacks; Joyce felt overburdened and underappreciated. Their feuds, their long bouts of coldness, inspired some of the most Thurber-like stretches of “Peanuts” — the strips where Charlie and Lucy seem to be locked in the eternal struggle of male and female, with the latter always wielding the upper hand.

As Schulz grew into middle age, he filled out, stopped wearing his hair in a buzz cut and discovered that he was actually attractive to women. He had one full-fledged affair, and in 1973, a year or so after divorcing Joyce, he married Elizabeth Jean Forsyth, 16 years his junior, whom he had met — where else? — at the ice rink. This second marriage was happier, in large part because Jeannie, as she was known, saw it her job to make it so. Schulz was often moody and withdrawn nevertheless, and was also compulsively flirty. The evidence suggests that his was essentially an arrested sensibility, locked in adolescent longing and self-absorption. But for a certain kind of artist this is not such a bad thing. Kipling and P. G. Wodehouse suffered, or benefited, from much the same condition: like Schulz, they were truly happy only when transported by their work. Schulz said once that if it weren’t for cartooning he’d be dead, and indeed he died within days of resigning from the strip because of ill health.