During the early-1960s, automakers were exploring new ideas in the personal luxury and specialty car segments. Chrysler, fast to enter the specialty car market, selected their Dodge Division to enter the marketplace with a bigger model to fit between the "pony car" Ford Mustang and the "personal luxury" Ford Thunderbird. The intention was to use the B-body for a sporty car with fastback look while sharing as much of their existing hardware as possible.
The fastback Charger was introduced in mid-season of the 1966 model year "in retaliation to the AMC Marlin, Ford Mustang, and Plymouth Barracuda", but even though based on the existing Coronet, "it was style-wise a complete departure from the Dodge's mainstream cars." The 1965 Rambler Marlin, along with the Dodge Charger that arrived during the 1966 model year, were "the two cars set the standard for radical fastback design in American mid-size automobiles." According to Richard M. Langworth, "because it was an intermediate like the Rambler Marlin, the Charger could have been an aesthetic disaster, but long side windows prevented its sweeping roof from looking too heavy."
Source: Wikipedia (original)