Joel Cairo works for Casper Gutman and is portrayed as a wimpy, delicate, sleazy "fairy." The character of Joel Cairo was based on a criminal Hammett arrested for forgery in Pasco, Washington in 1920. Hammett uses typical and offensive stereotypes of homosexuals as effeminate or womanish, which we can see in the opening description of Cairo's physical appearance:
The girl returned with an engraved card—Mr. Joel Cairo.
"This guy is queer," she said.
"In with him, then, darling," said Spade.
Mr. Joel Cairo was a small-boned dark man of medium height. His hair was black and smooth and very glossy. His features were Levantine. A square-cut ruby, its sides paralleled by four baguette diamonds, gleamed against the deep green of his cravat. His black coat, cut tight to narrow shoulders, flared a little over slightly plump hips. His trousers fitted his round legs more snugly than was the current fashion. The uppers of his patent-leather shoes were hidden by fawn spats. He held a black derby hat in a chamois-gloved hand and came towards Spade with short, mincing, bobbing steps. The fragrance of chypre came with him. (4.132)
Notice the specific details in this paragraph: Cairo walks with "mincing, bobbing steps." He smells of chypre, a fragrance that is both citrusy and earthy. And he's wearing fancy gloves, a tailored suit, and patent-leather shoes. (If you want to see Cairo in action, check out this clip of Peter Lorre's performance in the 1941 film adaptation of the novel).
Hammett's description of Cairo is a pretty unflattering and offensive portrayal of homosexuality. Cairo comes off as neat and meticulous when it comes to his clothes and the way he dresses. But in this case, Cairo isn't like the lovable Carson from Queer Eye for the Straight Guy or style guru Tim Gunn in Project Runway (we can't really picture Cairo saying "Make it work" to Spade....).
In The Maltese Falcon, Spade is clearly suspicious and scornful of Cairo's appearance. Does Spade feel threatened by Cairo's homosexuality? In fact, many people have accused Hammett of being homophobic in these descriptions. Is Cairo a negative example of the dangers of homosexuality, or is Hammett simply providing a contrast to Spade's aggressive masculinity?
We know very little about Cairo's motives in the novel. We assume that he works for Gutman because he's in it for the dough, so he is ruled by greed to a certain extent. But what's more important to note is Cairo's blatant affection for Wilmer, who we guess is his lover. When Spade tries to convince Gutman to use Wilmer as the scapegoat, Cairo is the first to defend Wilmer. And after Spade knocks Wilmer unconscious, Cairo frets over him, petting his hair and anxiously trying to revive him.
Even though the novel pretty clearly looks down on homosexuality as unnatural and depraved, it is obvious that Cairo's feelings for Wilmer are genuine and heartfelt, something which can't be said of many of the other relationships in the novel.