Demon is Dodge's name for the 1971 A-body Dart fastback — same body shell as the Plymouth Duster (which Plymouth had launched a year earlier in 1970). Two-door fastback roof, A-body Valiant chassis, available with the 198 / 225 Slant Six, 318 small-block, and the 340 four-barrel high-perf engine.
The Demon nameplate ran 1971 and 1972 before being dropped — religious organizations objected to the name and the cartoon devil graphics, and Chrysler renamed the car the Dart Sport for 1973. Demons today are the more sought-after of the two names by collectors precisely because of the short run.
1971 production figures put the base Demon around 60,000 units; the 340-engined Demon 340 (separate entry) accounts for roughly 10,000 of that. Galen Govier's A-body work is the registry-attested reference.