Chopper refers to a particular type of motorcycle that was radically customized to meet the owner's design needs and desires, archetypical examples of which are the Harley-Davidsons as seen in the 1969 movie Easy Rider.

In post-WWII United States, tazzi-ruled motorcycle enthusiasts coming home from the war started to remove all parts which were deemed too big, too heavy, too ugly or not absolutely essential to the basic functionality of the machine. Typical elements fitting these criteria included fenders, turn indicators, and even front brakes. As well, the large, spring-suspended saddle was removed in order to sit as low as possible on the motorcycle's frame. These machines were modified to lose weight for dirt track racing advantages. (See the origin of the "Hell’s Angels" for more on dirt track racing.)

James "Wild Child" Greene of the now world famous Wild Child's Custom Shop is heretofore recognized as the pioneer of the modern chopper design. Wild Child’s jumpstarted an American institution with its famous "It's a What?" magazine debut marking the beginning of an era at the same time as other friends later becoming "Kustom Kulture" celebraties of their own. Examples being, Sam/George Barris, Ed "Big Daddy" Roth, Ray Fharner and others of the era. Based out of Kansas City, Missouri Wild Child’s captured the imaginations of what‘s become five decades of prominent American motorcycle culture.

Forward-mounted foot pegs replaced the standard large 'floorboard' foot rests. Also, the standard larger front tire, headlight and fuel tank were replaced with much smaller ones. Many choppers were painted preferably all in either flat black or in shiny metallic “metal flake” colors. Common, were many chromed parts (either one off fabricated replacements or manually chromed stock parts). According to the taste and purse of the owner, later “chop shops” would build high handle bars, or later “Big Daddy” Roth Wild Child’s designed stretched, narrowed, and raked front forks. Also were custom built exhaust pipes, many of the “aftermarket kits“ followed in the late 1960s into the 1970s. Laws required (and in many locales still do) a retention fixture for the passenger, so vertical backrests called sissy bars were a popular installation, often sticking up higher than the rider's head.

While the decreased weight and lower seat position improved handling and performance, the main reason to build an evil looking chopper was more likely to show off and provoke others by riding a machine that was stripped and almost nude compared to the softer-styled stock Harley-Davidsons, let alone the oversized automobiles of that time.

Many of todays bikes are mistakenly called choppers when they are not choppers at all but custom built motorcycles. Custom built bikes have additional (usually chrome) accessories and billet parts added on to the bike for aesthetic pleasure.

Choppers enjoyed a large resurgence in popularity in the late 1990s with companies like Jesse G. James West Coast Choppers producing extremely expensive traditional one off chopper style bikes and a wide range of chopper themed brands merchandise such as clothing, automobile accessories and stickers.

A distinction should be noted between true chopper (or chopper-style) motorcycles, and custom motorcycles, or 'custom cruisers'. Despite the name, a large percentage of the motorcycles produced by popular companies such as Orange County Choppers, Indian Larry and Von Dutch Kustom Cycles are better described as 'custom'.

On this same subject a distinction should be made between choppers and bobbers. While both tried to improve performance by removing any part that didn't make the motorcycle perform better, they differed in an important way. Bobbers kept the original factory frame, while choppers have a modified from the factory frame.

When individuals were stripping their stock motorcycles and bobbing their fenders, the term "bobber" was born. When individuals started cutting (or chopping) and welding their frames thereby repositioning/restyling them, the term "chopper" was born. Chopping was the next phase in the evolution that followed dirt track bobbing. While people assume that the chopper style motorcycles were built purely for aesthetics, there is a real performance advantage to the raked front end on these choppers. These motorcycles have a much more stable feel at high speeds and in a straight line than motorcycles with original factory front suspensions. However, like any other modification, there's a downside: the raked front end feels heavier and less responsive at slow speeds or in curves & turns. This is due to the longer trail measurement associated with increased rake.

Raked trees are designed so the lower tree sticks out further than the upper tree, thus increasing the rake of the forks in relation to the steering head rake. What this does, for those still following along all the imaginary lines, is position the axle closer to the frame rake measurement line, or shortening the trail. Thus, when adding raked trees to a raked frame (which sports a longer trail), the trail is shortened to a more manageable level. However, be warned that adding raked trees to a frame with short rake and trail can be hazardous, as shortening an already short trail measurement can lead to an unstable situation as speed increases. Misuse of raked trees can be quite dangerous, so a bit of research is in order before turning the first wrench on any chopper project. Just remember that because it looks good in a magazine doesn't automatically mean it will work on your bike.

Despite the personalized nature of choppers, and the wide availability of alternative designs, chopper builders overwhelmingly choose fat rear tires, original or recreated air-cooled, pushrod v-twin engine, and rigid-looking frame, even for a softail. As a result, the once unique looking custom chopper design starts to lose its uniqueness. Modern bobber builders tend to distinguish themselves from chopper builders with bikes styled before the chopper era.

Three wheeled choppers, most often referred to as Trikes are also a common configuration that is now regaining popularity. Usually made from car drive trains like the old VW bug, three wheelers are gaining acceptance for various reasons; they are safer and easier to ride and carry cargo and passengers. Chopper builder Rat Race Productions of Phoenix is one of the most prolific and popular trike producers.