The file
A taco with the shell swapped for a hamburger bun. The Bell Beefer was Taco Bell's answer to the kid who wouldn't eat a taco, and it developed a following far beyond that kid.
When the chain sharpened its identity in the late '80s, the burger-shaped thing went. It has become the single most-requested item in Taco Bell's own social-media replies, and the company has teased it back more than once.
Sources: Wikipedia — Taco Bell