The original owner of the dial is Robert "Robby" Reed, a teenager from Littleville, Colorado, who discovers the dial in a cavern. Resembling an old telephone dial, this device is hand-held and covered in unknown symbols (that somehow Robby was able to understand as modern letters.) How the dial got there or who created it is never revealed. Each time he dials the letters H-E-R-O, Robby finds he turns into a different superpowered being; dialing O-R-E-H makes him revert to his normal form. He quickly uses it to protect Littleville under the guises of numerous superheroes.
Robby's H-Dial was once used by his foe, Daffy Dagan, who  briefly becomes a supervillain known as Daffy the Great after dialing V-I-L-L-A-I-N. In House of Mystery #169 (September 1967), Robby's girlfriend Suzie uses the dial, dialing H-E-R-O-I-N-E to temporarily transform into Gem Girl. At the end of the story Suzie receives a blow to the head that causes her to forget about the secret of the device.
Chris and Vicki
Two other dials are discovered years later by teenagers Christopher "Chris" King and Victoria "Vicky" Grant of the New England town of Fairfax in a 'haunted' house. These dials--disguised as a watch and a necklace--only have the letters H-E-R-O on them, and work only for an hour, after which they will not work for another hour. King and Grant begin protecting Fairfax from a number of menaces. Unknown to them, most of these villains are created by a mysterious villain known only as The Master.
Eventually Chris and Vicki discover that a fellow student named Nick Stevens has been drawing up superheroes as a hobby--and somehow, the dials turn them into those heroes. With Nick's help, they find out that their dials were created by a being called The Wizard (not to be confused with the villain of the same name), whom the Master thought he'd killed years before. In truth, The Wizard faked his death while he looked for the original Hero Dial. With it, he merges with The Master--and transforms into Robby Reed, who explains that years before, he had used the dail to split in two so that he could disarm a dead man's switch, while his other self, the Wizard, defeated the villain who set it.
However, the Wizard carried all of Robby's inherent goodness, while the Robbie that remained possessed only evil impulses; the original Hero Dial was lost when this Robby, renaming himself The Master, dialed "hide yourself", causing the dial to vanish along with The Master's and The Wizard's memories of their former life as Robby Reed. While The Master learned genetic techniques that allowed him to create his army of super-villains, the Wizard was driven to create the new H-dials, unconsciously designing limitations into them to prevent what happened to Robby from recurring (only heroic identities, a time limit, and the exclusion of letters other than H-E-R-O; the latter, however, did not prevent Chris from experimenting on one occasion and dialing H-O-R-R-O-R, with disastrous results). With Nick developing the ability to actively influence the dials' results (rather than subconsciously as before), Robby passed his dial to Nick, and retired as a hero, though he would seek it out again many years later according to one account.
King and Grant later demonstrated the ability to internalize the Dials' powers, presumably due to extended exposure, though not without side effects: Grant became mentally unstable, while King found himself unable to control his transformations. Grant's H-Dial was eventually discovered by the Scavenger (who seemed to realize it was not unique (he expressed irritation that 'someone' kept on making these things), though he did not elaborate on the Dials' origins) and fell into the hands of Hero Cruz, who used it to gain super powers and later to aid Grant in regaining her sanity.
The original H-Dial, or something which looked like it, was later seemingly destroyed by Alan Scott, the original Green Lantern.
Robby Reed's eventual recovery of the Dial in the 2003 series H.E.R.O may or may not still be in continuity. No specific dates are ever given for the events.