Short form of Edward or Edmund, from Old English 'ead' meaning wealth or fortune.
Ed is the most elemental reduction of a cluster of Old English names — Edward, Edmund, Edwin, Edgar — all built on the element ead, meaning "wealth," "fortune," or "prosperity." To be named Ed in the Anglo-Saxon tradition was to be named for good fortune itself, a monosyllabic wish condensed to almost nothing. The English royal line made Edward one of the most durable names in the language: eight kings of England bore it, from Edward the Confessor in the 11th century through Edward VIII, who abdicated in 1936.
Ed, as the casual form, carries all that heritage without any of the weight. As a standalone given name, Ed was common enough throughout the 19th and early 20th centuries that it belonged to a vast and varied cast of American life. Ed Sullivan shaped American television culture for twenty-three years.
Ed McMahon was the archetypal loyal second, Johnny Carson's sidekick for thirty years on The Tonight Show. e. cummings, playing with the very letterforms of his name.
Ed Gein, notoriously, became synonymous with a particular strand of American gothic horror, illustrating how thoroughly a name can be recontextualized by a single bearer. In literature and film, Ed is often the everyman — the name given to characters who are decent, somewhat ordinary, occasionally surprising. It carries no social class marker in the way that names like Reginald or Chester do.
By the late 20th century, Ed had become slightly retro, associated with fathers and grandfathers rather than newborns. That retro quality is now, predictably, part of its appeal. Short, legible, impossible to misspell, and backed by centuries of royal and common usage alike — Ed is the name that has always worked and never needed to explain itself.