Biography
A Longcoat is the ideal action-hero garment, more practical than a cape but infinitely cooler than a sport coat or no coat. Also, a Longcoat of any level of "billowy-ness" makes an ideal cover for producing any number of weapons, tools, supplies, and whatnot. Certain styles of Longcoat are deliberately designed to distort the wearer's frame, making their wearer's access to Hammerspace almost believable to mundane eyes. This distortion of the wearer's real shape also makes it genuinely harder to land an accurate attack on them.
Like capes, longcoats capitalize on the dramatic effect of having something that flutters behind you. It's especially effective in animated or drawn material, where the coat can be shown billowing a lot more than it could in real life (and a lot more stylishly) — to the point that it really does look like a cape. A variant involves jackets and excessively long shirts, but having less material to billow in the gusts necessarily makes such people seem less badass. And of course, when the wearer of a Badass Longcoat takes the coat off, it's a sign that he's about to do some major damage — he just doesn't want to get your blood on his coat. Additionally, a longcoat in fiction is rarely worn closed, and many are cut in such a way that closing them is impossible, giving the illusion of a broader chest and more masculine figure.
The most common types of long coats are dusters, trench coats and frock coats.◊
Dusters are longer overall, usually reaching nearly to the ankles. Since they're designed for horseback riding, they have a long slit up the back as far as the waist, and optional leg straps so they don't billow too much in the wind or while riding. Dusters are also generally cut along fairly boxy lines.
A trench coat, on the other hand, is usually more shaped, reaches to the knees or slightly below and the back slit generally only reaches mid-thigh or hip-level. Trench coats also usually feature a belt and epaulets. It should be noted that one way to tell if a trench coat indicates a spy or private investigator or is a Badass Longcoat is by whether it's buttoned and belted or not. A Badass Trenchcoat is never closed (unless it's on Humphrey Bogart).
An older variant of the trenchcoat is the greatcoat, a predecessor of the trench coat but usually much heavier, and with either a wider collar that can be turned up to protect against the wind or a short shoulder cape. Later greatcoats lost the cape, becoming a longer, heavier, double-breasted overcoat, but retaining the name. Greatcoats were typically worn either buttoned, losing some of their badassitude for style, or simply draped over the shoulders without putting the arms into the sleeves, greatly increasing their badassitude. They're most often associated with 19th Century naval officers, Nazi SS officers, and Russian soldiers.
The Inverness cape◊ is a lighter garment with a very similar appearance to the caped greatcoat. The cape, however, is longer, reaching slightly past the wrist rather than only to the elbow, and an Inverness cape has no sleeves at all.
Frock coats, in contrast to all of the above coats, are very exquisitely tailored coats usually made of wool, like a longer version of a sport coat, but much more formal. Variants also include, on occasion, materials such as leather and, depending on the time in which the piece takes place, even silk. As they are one of the most enduring and universal fashions in the history of men's clothing, they have many different variations in cut ranging from the square-cut military frock coats◊ of the 1600s to the cutaway-style frocks◊ of the mid-to-late 1700s, to the, again, square coats that every Victorian and Edwardian aristocrat can be seen wearing in all of your favorite period dramas. In all of these cases, the coat is not intended to be closed — most of the time they don't have buttonholes — although from the later 1790s through to around the 1870s, and later on in the 1920s, they could be worn either way. If you're watching a period piece from the 1600s to the start of World War II, chances are most, if not all, of your male characters are wearing some kind of frock coat.
Please note that they are not in any way overcoats.
Being that they are tailored, with pleated tails that reach down to around the knees and pleated vents that invariably end right at the waist (beneath two buttons sewn in for decoration), frock coats have a tendency to sway and billow as one walks or stands facing the wind, without the heaviness or general shapelessness of leather or canvas, which are the two materials that most trenchcoats, greatcoats, and dusters are made from.
Moby-Dick features the "long-togged Scaramouche" (an evangelical preacher who has gained moral ascendancy over his crewmates) and Oliver Twist has The Artful Dodger, making this at least Older Than Radio.
Going back even further is a coat called a Justacorps (essentially the long coats of the 17th and 18th centuries; think Pirates of the Caribbean), though it has to be worn a certain way to pull off the badass look.
A less modern example would be the Badass Long Robe. Cool Shades are a nice accessory, as are tacking on some Signature Headgear and a Cool Mask to achieve the Coat, Hat, Mask Effect. If the mask in question is a gas mask, then it's Gas Mask, Longcoat. The Badass Longcoat is often combined with a pair of guns, either revolvers for a western or a pair of semiautomatic pistols or submachine guns in the modern-day and beyond, for extra effect. Some characters will pack enough weapons in their longcoats to outfit a small army.
Longcoat-wearing heroes probably started with Westerns (for dusters) or Film Noir (for the classic trenchcoat), but became especially common in the public mind after The Matrix.
The Badass Longcoat is closely associated with Those Wacky Nazis (since Germans in war have been associated with wearing leather longcoats), The Stoic, the Trenchcoat Brigade, and (thanks to the Columbine High School massacre) the Spree Killer. Compare Badass in a Nice Suit, and contrast Not-So-Badass Longcoat. Not related to Badass Longcat. Not to be confused with Conspicuous Trenchcoat, a specific type of coat that is also long, or Coat Cape, where a coat is worn over the shoulder like a cape for what is often a similar visual effect.
(Please note that this trope is about the coat, not the person. Please include information about the coat when adding examples, rather than simply listing a character. The coat is important.)