Mike Campbell, a Scottish war veteran, is a friend of Jake’s as well as Brett’s fiancé. These relationships put him in the middle of the ever-growing tension among the men over Brett’s affections, a position which inevitably exposes his aggressive attitude. Almost always drinking, Mike grows increasingly hostile toward those around him as he gets more drunk, and this antagonism contributes to the climactic moment in which Cohn attacks him and Jake. Leading up to this fight, however, are many scenes in which Mike berates Cohn. Jake and Bill make jokes at Cohn’s expense as well, but Mike’s are deeply personal and have a harsher tone. Many of his comments carry an antisemitic sentiment, for example, and this approach emphasizes both his inherent prejudice and his willingness to employ malicious tactics to assert his superiority. One of the reasons that Cohn in particular draws Mike’s ire is because of his affair with Brett in San Sebastian. While Hemingway seems to imply that Brett has had affairs with numerous men during her engagement, Mike struggles with the fact that Cohn sticks around long after the trip to San Sebastian ends. His presence serves as an ongoing reminder to Mike that he lacks control over his relationship, leading him to feel that his masculinity is under threat. Brett’s interest in Romero further exacerbates Mike’s sense of inferiority, and this development inspires more drunken rage.

In addition to his relationship struggles, the apparent purposelessness of Mike’s life makes him a particularly miserable character. The fact that he is bankrupt and without a job symbolizes the emptiness of his existence, leaving him with nothing to do except drink endlessly. Hemingway implies that Mike awaits a large inheritance that will one day make him rich, but this promise seems too abstract and far away to bring any kind of meaning into his life. Even when Mike’s time was occupied as a soldier during the war, his admission to the group that he once handed out military medals at a nightclub emphasizes his lack of care. Of all the characters in the novel, Mike is perhaps the clearest representation of what it means to be a member of the Lost Generation.