"Most people think Marv is crazy. He just had the rotten luck of being born in the wrong century. He'd be right at home on some ancient battlefield swinging an axe into somebody's face. Or in a Roman arena, taking his sword to other gladiators like him. They woulda tossed him girls like Nancy back then. "
Lightning Bruiser: Despite his size, Marv is just as quick and agile as he is strong. There are several instances where he takes down multiple opponents in a short span of time and even avoids getting shot.
Not Good with People: Between his frightening appearance and mental instability Marv doesn't seem to do well with people, but he outright refuses to kill a wolf, instead knocking it unconscious and giving it a gentle pat.
Wouldn't Hit a Girl: Marv is really big on this, possibly due to his upbringing. The only times he breaks this is to spare Wendy from watching him torture Kevin to death, and killing a female sex-slaver in one short story.
Once ventured into Type IV territory when he considered shooting a cop even though he wasn't sure he was clean or not. Generally, however, he's a normal guy who has been squicked out by the actions of both Marv and Miho.
Badass Bookworm: He is well-read, going by his knowledge of Spartan battle techniques and the fact that he apparently knows Latin.
Would Hit a Girl: Though Dwight is violently protective of women, he is not above hitting them, whether because they deserve it (such as Ava) or because he needs to snap them out of hysterics (such as Gail).
Improbable Aiming Skills: He shoots sniper through the scope of his own rifle, using a regular handgun while in a dark room. Later, he kills an entire warehouse full of mooks before any of them have the chance to fire a single round.
Nice Guy: Amazingly nice, given the sheer ruthlessness and ugliness of the setting. It's notable that he gets one of the few truly happy endings in the entire comic series.
Wallace seems to be one of the most formidable fighters in the entire setting. While sheer numbers and firepower seems to give all but the most deranged of Sin City protagonists (Marv) some pause, all Wallace needs is a small amount of time to get some guns, and he is perfectly capable of dismantling a large part of a criminal organization, and is considered by their Genre Savvy leader to be "too costly" to seek revenge against.
Sociopathic Hero: She does things that make even the more hardened of the girls of Old Town go "Yeesh!"
The Stoic: Miho has no expression on her face other than a deadly calm when she goes to work.
Tsundere: In Family Values, her softer side is shown when she cuddles up and goes to sleep on Dwight's lap and seems to have a very comfortable demeanor around him, in contrast to her earlier depictions where she is moments away from slicing him in half. Whether or not there is romance is up for debate. It hasn't stopped fans from Shipping the two of them.
It's also a nod to her being frequently described as "catlike" in her mercurial attitudes and casual cruelty.
Spoiled Brat: Hartigan calls him this many times and it seems to be true. He whines when he doesn't get his way and at one point, threatens a Mook that he will call his father if his Torture Cellar wasn't set up properly.
Badass: Not only is he one of the few badguys that lives through more than one story, but he is the only one to survive confrontations with Miho, Marv, and Wallace. In fact, surviving a confrontation with just one of these people is badass enough, to say nothing of all three of them.
Expy: Given his tendency to wear single-color suits (usually white), his immense size, and his baldness, it's possible that he's basically a German version of the Daredevil villain Wilson Fisk, the Kingpin. It's notable that Frank Millar did some of his better known early work in comics on Daredevil.
Genre Savvy: It's possible that this is the reason he's such an effective mob boss. Ava Lord is an obvious Femme Fatale, and while her seemingly supernatural ability to attract and manipulate men works on seemingly everyone, he simply tells her right away that "her charms didn't interest him". Furthermore, after Walter deals a heavy blow to his operations, he simply tells his lieutenants that it would be too costly to go after the obvious heroic protagonist One-Man Army.
The Ghost: In many stories, he is mentioned and you can even see his plans coming to fruition but he never pops in. In fact, he never comes face-to-face with any of the heroes in Sin City, luckily enough.
Money Tropes: Hard to say just how many of these he fits, but he's a chilling villain who puts the "organized" in Sin City's organized crime, without ever even being threatened by any of the heroes, and he doesn't care about anything but making a profit.
Nazi Hunter: If the fan theory about him is true. See WMG for more details.