No detective story would be complete without the bad guy, and Eddie Mars comes ready dressed for the part. Our first look at Mars reads like we're watching a movie in black and white, or more accurately, in shades of gray:
He was a gray man, all gray, except for his polished black shoes and two scarlet diamonds in his gray satin tie that looked like the diamonds on roulette layouts. His shirt was gray and his double-breasted suit of soft, beautifully cut flannel. Seeing Carmen he took a gray hat off and his hair underneath it was gray and as fine as if it had been sifted through gauze. His thick gray eyebrows had that indefinably sporty look. He had a long chin, a nose with a hook to it, thoughtful gray eyes that had a slanted look because the fold of skin over his upper lid came down over the corner of the lid itself. (13.58)
Aside from the fact that this is pretty cool physical description of the villain, why does Marlowe spend so much time giving us these minute details about the way Mars is dressed? First, we know that he's loaded: his shoes are well polished, he wears diamond tie pins, and his suit is perfectly tailored. Second, he's crazy polite: as soon as he sees Carmen, he removes his hat (whether or not it's genuine is beside the point). And finally, his eyes are described as simultaneously "thoughtful" and yet with a "slanted look" which hints at his role as a dishonest crook.
And as a dishonest crook, Mars pretty much epitomizes everything that Marlowe despises. He's the owner of the Cypress Club, a ritzy gambling house on the beach (and Vivian's favorite hangout spot). As a racketeer, Mars is totally unscrupulous, and he's somehow involved in nearly every single murder that occurs in the novel. But of course he's got connections with the fuzz, so he's never charged with any of his crimes. To be fair, he's just one of many folks in the novel who get off scot free despite their dirty dealings, which shows us just how corrupt, inefficient, and nasty the justice system has become in Chandler's America.
Marlowe sums up his poor opinion of Mars in his conversation with Mona:
"You think he's just a gambler. I think he's a pornographer, a blackmailer, a hot car broker, a killer by remote control, and a suborner of crooked cops. He's whatever looks good to him […] Don't try to sell me on any high-souled racketeers. They don't come in that pattern." (28.49)
Marlowe is critical of Mona's denial regarding the true nature of Mars, so he bluntly lists every single one of Mars' illegal interactions (suborner means briber, in case you were wondering). Marlowe later adds that Mars "never killed anybody, he just hires it done" (28.75). The fact that Mars always hires someone else to do the actual killings allows him to keep his own hands clean. It also means that a murder can never be directly pinned on him, and he's able to get away scot-free. So even though Mars never pulls the trigger himself, it's pretty clear that he is mixed up in several of the deaths that take place in the novel. And at the end of the novel, all we know about Mars's fate is that he never gets punished. So much for justice.