Here's a shocker: Bill is... actually pretty happy and likeable. And he's a character in The Sun Also Rises.
Take your jaw off the floor. There had to be at least one sympathetic character in this novel.
Since Bull and Jake have a close bond, we see him in a friendly light, despite some of his unsavory tendencies. He, like Jake, is a productive working man; he writes books that are apparently somewhat successful (his European trip follows on the heels of a financial windfall from his last book). He’s sort of a mirror image of Jake—they have many similarities, such as their war experiences and their dedication to work, but Bill is also Jake’s opposite in that he emerged physically unscathed from the war, and chose to return to America, rather than stay in Europe.
In fact, Bill thinks that a lot of Jake's problems have to do with his decision to stay in Europe:
"You’re an expatriate. You’ve lost touch with the soil. You get precious. Fake European standards have ruined you. You drink yourself to death. You become obsessed by sex. You spend all your time talking, not working. You’re an expatriate, see? You hang around cafés."
"It sounds like a swell life," I said. "When do I work?"
"You don’t work. One group claims women support you. Another group claims you’re impotent."
"No," I said. "I just had an accident." (12. 13)
On the outside, Bill seems like a stereotypical hard-boiled, witty Hemingway stock figure, but once he and Jake leave the boundaries of the city, we begin to see him in a different light. He shares a profound appreciation for the natural world with Jake, and their friendship is depicted as one of the only genuine relationships in the novel. The scenes of their idyllic trip to Burguete, where they meet another like-minded outdoorsman, Harris, are the most contented moments we witness in the novel.
After the fiasco of Cohn, Brett, and Romero plays out in Pamplona, the only truly stable relationship that emerges unaffected is that of Bill and Jake. Bill is a faithful standby, a true companion and loyal friend.