Jason Segel is the affable Judd-Apatow-comedy-troupe alum who has gone on to headline nine seasons of How I Met Your Mother, reboot the Muppets, and co-star with Cameron Diaz in this July's Sex Tape comedy. Despite his Hollywood successes as a writer, producer, and actor—and his dramatic departure as David Foster Wallace in the upcoming biopic The End of the Tour—Segel seems to identify most with the awkward, adolescent iteration of himself that inspired his first literary effort, Nightmares!: a young-adult trilogy co-authored by Kirsten Miller, the first installment of which arrives in bookstores in September. Here, a compendium of the 34-year-old's nocturnal memories, everyday preferences, and endearing peculiarities.

HE BEGINS each day with five or six cups of black coffee and only switches to water once he starts feeling ill.

HE IS right-handed when it comes to all activities except eating. At the table, he mysteriously becomes a lefty.

HIS FAVORITE meal is steak, which he's been eating less of since becoming more health-conscious around his 30th birthday.

UNTIL THE age of 10, he wore a Superman cape tied around his neck and covertly tucked underneath his clothes—just in case anything went awry in his Pacific Palisades, California, neighborhood.

AS A pre-teen, Segel had recurring nightmares during which he always fought Dracula inside the vampire's house, becoming very familiar with his nocturnal nemesis's floor plan: “I created this very cushy living-room environment [in my mind] where I could hide from Dracula and play video games.”

HE HAS no regrets about having worn a mustard-colored jacket and purple pants to his Bar Mitzvah, in the early 90s, “when that was totally acceptable to wear.”

HE IS in no rush to have any pets, especially after growing up with two dogs and six cats.

EVER SINCE watching the Muppets on television as a child, Segel has had a deep and abiding love for puppets. His first was “an old man named Walter,” which Segel recalls purchasing outside Faneuil Hall, in Boston.

HIS NICKNAME in high school was “Dr. Dunk”—because he was a “lean, mean” basketball-playing machine. After inheriting his parents' black Jeep Grand Cherokee, he briefly considered getting a “Dr. Dunk” vanity license plate but settled for a custom-embroidered “Dr. Dunk” baseball hat instead.

BORN AND raised in Los Angeles, he still lives there and keeps a second home in town strictly for writing, working, and housing his puppet collection—comprising between 15 and 30 figurines. “I used to live in there,” Segel says of the house, “and then I realized that it was incredibly creepy to have visitors over, because I just looked like a total weirdo.”

HIS BEST friend is Brian, a medical doctor living in New Haven, Connecticut, whom Segel has known since he was 13.

HIS FATHER recently retired as a corporate lawyer.

HE HAS two siblings, a brother named Adam, who is a money manager, and a sister named Alison, whom Segel calls a “relentlessly hilarious writer.”

HE DID not warn his mother that he appeared fully naked in the 2008 breakup comedy Forgetting Sarah Marshall, which he wrote, before she saw the film. Her reaction: “She cried,” he recalls.

SHE THEN sent out a mass e-mail to family members with the following warning: “I would like to inform you all that Jason has chosen to do full-frontal nudity, however, it is not gratuitous and is essential to the plot.”

HIS MOTHER has not needed to send out mass e-mail warnings about his films since.

HIS LIFELINE is an iPhone, which displays a Karl Kwasny illustration from Segel's forthcoming novel on the home screen.

WHEN IT comes to interior décor, Segel has “a real affinity for things that are, by any account, an old man's taste—a lot of dusty brown and corduroy.”

HE RETIRED his D.V.R. a couple of years ago upon realizing that TV prevented him from seeing classic films: “I just got around to seeing Citizen Kane, which blew my mind, and Singin' in the Rain.”

TO OFFICIATE a wedding on The Tonight Show in 2010 between two fans, he became an ordained minister by completing a two-minute Internet transaction.

HE PLAYS the piano, toys with a ukulele, and can teach himself a song on the guitar if you give him two weeks' notice. While he's never been in a band, he has performed onstage with Maroon 5 and the folk group the Swell Season.

HE DOES a lot of thinking between midnight and four A.M. and figures that he probably annoys his assistant most with flurries of random early-morning e-mails.

HE KEEPS in touch with Ted Walch, his high-school performing-arts instructor at Harvard-Westlake, to whom Segel says he owes his career.

HE CARRIES a framed photo of the late Oscar-nominated actor Peter Sellers to every film set to remind himself of his acting inspiration—a man whose dual ability to bring audiences to laughter and tears makes him indefinable in Segel's book.