Steel guitars were originally invented and popularized in Hawaii. Legend has it that Joseph Kekuku, a Hawaiian schoolboy, discovered the sound while walking along a railroad track strumming his guitar. He picked up a bolt lying by the track and slid the metal along the strings of his guitar. Intrigued by the sound, he taught himself to play using the back of a knife blade. Other persons who have been credited with the invention of the steel guitar include Gabriel Davion, an Indian sailor, around 1885, and James Hoa, a Hawaiian of Portuguese ancestry.
"Slide guitar" is a term used to describe how a guitar is played, namely, using a bottleneck or other glass or metal tube, or a flat metal object, such as a pocketknife, to dampen the strings. A Slide guitar could be either a regular, steel-stringed guitar, with raised frets, played vertically, or a high-string steel guitar (no resonator) or Dobro (with resonator), played with a slide (bar, tube, knife, etc.) Slide guitarists often uses regular tunings, or tune only the top strings into a chord.
Many country and bluegrass players use the Dobro® (or a resonator guitar), a steel guitar which uses an internal metal resonator (like a pie pan, with special bracing) to make it louder. "Dobro®" is a registered trademark of the Original Musical Instrument Company. Other resonator-equipped guitars are made by many different companies, including National, Melobar, Scheerhorn, and Johnson. You will sometimes see these referred to as "resophonic" or "ampliphonic" guitars. These are acoustic instruments which are loud due to the resonator that directs the sound outward. Some guitar makers construct instruments entirely out of metal, giving new meaning to steel guitar.
The steel guitar eventually mutated as players sought to expand its usage. The first mutation was adding electric pickups, creating the Electric Hawaiian steel guitar, or the electric lap steel. These were solid-body wood instruments that had no need for a traditional guitar shape. Then, additional strings were added, then additional necks. As the steel guitars got heavier, they were placed on legs, changing from lap steels to table steels. Finally pedals and knee levers were attached to the strings, allowing the player to change tunings and bend strings mechanically, as the guitar is played. The pedal steel guitar is the main steel guitar played today.
Noted Dobro/resonator players: