T uca and Bertie represent two halves of Hanawalt’s personality. Tuca is her id — the selfish, charming beast who comes out screaming in her art. Bertie is the first face that Hanawalt presents to the world — painfully introverted and exceptionally anxious. An early scene in “Tuca & Bertie” is borrowed from her relationship with the comedian Adam Conover, her partner of 10 years. When Bertie panics over a big presentation at her job at Condé Nest, her devoted boyfriend Speckle (voiced by Steven Yeun) pantomimes lightly massaging her with a “worry vacuum” to suck her anxiety away. But he gets so invested in the bit that he knocks over a glass and has to sheepishly fetch the real vacuum.

When Hanawalt pitched the show, she found the character’s anxiety difficult to communicate. Everybody wanted to know why Bertie was so anxious, and she could only say, “She’s anxious because she has anxiety.” Hanawalt has had anxiety for as long as she can remember. Growing up in Palo Alto, Calif., “I just didn’t feel like other kids,” she said. “I didn’t have fun at summer camp.” Drawing became her self-soothing mechanism, a way for her to stay calm and centered.

Hanawalt has always drawn animal-human hybrids; at school, she pretended that she was a horse. This did not help integrate her into the mainstream of child society, but privately she expressed confidence in her choice. As she wrote in a sixth grade class assignment: “People make fun of me an call me ‘Horse poop’ and ‘Lady Horse.’ I just take it as a compliment, or I figure that they must like Horse Poo a lot, cause I hear them say it whenever I pass!” She added: “I’m also wild about art. I want to be famous for drawing Horses someday.”

In high school, Hanawalt drew through every class. Though she struggled academically, she produced her own zine, “Lobster Rags,” and took to theater, which is how she met Raphael Bob-Waksberg, the future creator of “BoJack Horseman.” He directed weird plays; she built sets and made her acting debut as a dead body. Between classes, Bob-Waksberg would page through Hanawalt’s sketchbook and they would make up voices and stories for her characters. When their friends all started LiveJournals, Bob-Waksberg was most captivated by hers. “We all tried to put some version of our best selves on the internet,” he said, “and here was this girl just talking about her periods, and her acne and how horny she was.”

In 2010, after Hanawalt had gone to U.C.L.A. to study art and risen to prominence in the indie comics scene, Bob-Waksberg emailed to ask: “Hey, do you have a picture of one of your horse guys, by himself?” He wanted to use her illustrations to pitch an animated show called “BoJack the Depressed Talking Horse.” She agreed, but told him his pitch felt unnecessarily cynical. “Maybe there’s a way for BoJack to not be too much of a bummer?” she wrote back. “Just a thought, I’m not an Eeyore fan.”