Being that Terence Winter was an integral writer on The Sopranos, every time i watch Boardwalk Empire i notice how many of its characters seem to occupy similar roles as the characters from Sopranos.
Nucky - I'll start off kind of weakly here by saying that outside of the obvious parallels between Nucky and Tony Soprano, they really are fundamentally different characters. the physicality, to begin with, is pretty much the exact opposite. I mean, come on, compare everything about Steve Buscemi to everything about James Gandolfini. The only real similarities between the characters are their relationships to other characters, as well as the basic premise that they are the "boss". His character arc, a politician turning into a gangster, is quite different from anything we've seen. in a way he's kind of a reversal of Stringer Bell from The Wire.
Margaret - Definitely Carmela, for the most part, with a hint of Melfi. Her conflict, like Carmela's, was between the safety and luxury of her life under an evil man's thumb, and the moral conflict of being with such an evil man. Like Melfi, though, she has managed to break away from this man (at least for now, this could turn back into Carmela territory if she gets back with Nucky), and is a kind of feminist figure in the show. She also suffered an act of horrific violence in the pilot that could be compared to Melfi's rape in "Employee of the Month". these are comparable in that, while Melfi actively refrained from siccing Tony on her rapist, Nucky found out about the beating on his own and had Margaret's husband killed. Like Melfi, Margaret had a fundamental moral opposition to this act.
Jimmy - Jimmy has clear parallels with Christopher in his relationship with Nucky, and his character arc is somewhat similar to a condensed, amped up version of Chris, in which he rebels against his mentor, who murders him. However, Jimmy's rebellion was actually intentional and he followed through with it, whereas Chris just stagnated under Tony's thumb and acted out, antagonizing him. Their mini arcs in the first couple episodes of their respective series are pretty similar as well - Chris hijacks trucks without Tony's go ahead, resulting in a mock execution, and Jimmy steals liquor shipments without Nucky's go ahead, forcing him to leave town. In the structure of the show, he could be compared to Big Pussy - each being a character close to the protagonist whose death in the Season 2 finale signaled that this show means business.
Van Alden - Van Alden is unlike any character from The Sopranos. He could most accurately be described as a weird mashup between McNulty from The Wire and Brother Justin from Carnivale.
Eli - Eli is quite similar to Christopher in many ways, as the protagonist's younger relative who is a constant thorn in his side, yet whom he continually spares. Eli as a person has more similar character traits to Chris than Jimmy did. Whereas Jimmy is a purely tragic and solemn character, Eli engages in the kind of absurd farce we sometimes saw with Christopher.
Richard Harrow - Really unlike any Sopranos character, except maybe Baccala in a really vague way, as their story arcs each deal with the character emerging from his shell. He might also be comparable to Omar Little as a sort of "wild card" outsider character.
Gillian - Gillian, for the role she plays in the story, could probably be compared to Livia. She serves as a specter of guilt hanging over both Nucky and Jimmy, as Livia was to Tony. She also has elements of Janice in the absurdity of her conceit and delusion and the rabid hate the fanbase seems to have for her. Though the character model of Gillian is generally more of an elaboration on characters like Atia of the Junii in Rome than any Sopranos archetype.
Chalky - If I had to compare Chalky to a Sopranos character, it would probably be Silvio. Chalky is generally the most loyal of Nucky's allies, and is a cool motherfucker. The comparison to Silvio is not perfect, though. His major conflict, the clash between the privileged life he gives his family and the brutal world where he built that life, is kind of similar to Tony Soprano.
Arnold Rothstein - Comparable to Johnny Sack, as a constantly fluctuating friend/enemy of the protagonist, and a gangster from another town.
Al Capone - His depiction draws heavily from Tony Soprano. Outside of that he's not really similar to any character on a previous HBO series.
Lucky Luciano, Meyer Lansky - Also quite unlike any other characters from an HBO series.
Eddie Kessler - Also a comparison to Silvio, as Nucky's utterly loyal, ever present subordinate.
Owen Sleater - Furio. Both Europeans from the protagonist's home country who are brough over and fall for the boss's wife. Their respective exits from the show are similarly understated - Furio just vanishes, Owen is killed off screen. Their exits are also what drive the biggest rift between the boss and his wife.
Lucy Danziger - Irina.
Gyp Rosetti - As a character who brings an unforseen level of evil and villainy to the show in its third season, Gyp is comparable to Ralph Cifaretto. As a pretty standard one-season "Big Bad" he would be more comparable to Richie Aprile.
Manny Horvitz - Also comparable to Richie Aprile, since Manny's bloodlust and decaying relationship with a protagonist drive a large part of the plot in each show's second season. They mirror each other in an interesting way, as well - Manny killed Jimmy's wife, while Richie was killed by his own wife, both of these being major unexpected game changers for the stakes of the shows.
Mickey Doyle - Paulie Walnuts. Both being absurd, comedically stooge-like villains.
The Commodore - Sort of an amalgam of Livia and Junior, as the bitter old mentor who turns on his protege.
Taps, lights out, 2200 hours. What's missing? Give up? Television.