Many experiments at electrically amplifying the vibrations of a string instrument were made dating back to the early part of the 20th century. Patents from the 1910s show telephone transmitters were adapted and placed inside violins and banjos to amplify the sound. Hobbyists in the 1920s used carbon button microphones attached to the bridge; however, these detected vibration from the bridge on top of the instrument, resulting in a weak signal. With numerous people experimenting with electrical instruments in the 1920s and early 1930s, there are many claimants to have been the first to invent an electric guitar.
Electric guitars were originally designed by acoustic guitar makers and instrument manufacturers. The demand for amplified guitars began during the big band era; as orchestras increased in size, guitar players soon realized the necessity in guitar amplification & electrification. The first electric guitars used in jazz were hollow archtop acoustic guitar bodies with electromagnetic transducers. Early electric guitar manufacturers include Rickenbacker in 1932; Dobro in 1933; National, AudioVox and Volu-tone in 1934; Vega, Epiphone (Electrophone and Electar), and Gibson in 1935 and many others by 1936.
The first electrically amplified stringed instrument to be marketed commercially was designed in 1931 by George Beauchamp, the general manager of the National Guitar Corporation, with Paul Barth, who was vice president. The maple body prototype for the one-piece cast aluminium "frying pan" was built by Harry Watson, factory superintendent of the National Guitar Corporation. Commercial production began in late summer of 1932 by the Ro-Pat-In Corporation (Electro-Patent-Instrument Company), in Los Angeles, a partnership of Beauchamp, Adolph Rickenbacker (originally Rickenbacher), and Paul Barth. In 1934, the company was renamed the Rickenbacker Electro Stringed Instrument Company. In that year Beauchamp applied for a United States patent for an Electrical Stringed Musical Instrument and the patent was later issued in 1937.
Electro-Spanish Ken Roberts, 1935
By early-mid 1935, Electro String Instrument Corporation had achieved mainstream success with the A-22 "Frying Pan" steel guitar, and set out to capture a new audience through its release of the Electro-Spanish Model B and the Electro-Spanish Ken Roberts, which was the first full 25" scale electric guitar ever produced.
The Electro-Spanish Ken Roberts was revolutionary for its time, providing players a full 25" scale, with easy access to 17 frets free of the body.
Unlike other lap-steel electrified instruments produced during the time, the Electro-Spanish Ken Roberts was designed to play standing vertical, upright with a strap. The Electro-Spanish Ken Roberts was also the first instrument to feature a hand-operated vibrato as a standard appointment, a device called the "Vibrola," invented by Doc Kauffman.
 It is estimated that fewer than 50 Electro-Spanish Ken Roberts were constructed between 1933 and 1937; fewer than 10 are known to survive today.
The solid-body electric guitar is made of solid wood, without functionally resonating air spaces. The first solid-body Spanish standard guitar was offered by Vivi-Tone no later than 1934. This model featured a guitar-shaped body of a single sheet of plywood affixed to a wood frame. Another early, substantially solid Spanish electric guitar, called the Electro Spanish, was marketed by the Rickenbacker guitar company in 1935 and made of Bakelite. By 1936, the Slingerland company introduced a wooden solid-body electric model, the Slingerland Songster 401 (and a lap steel counterpart, the Songster 400).
Gibson's first production electric guitar, marketed in 1936, was the ES-150 model ("ES" for "Electric Spanish", and "150" reflecting the $150 price of the instrument, along with matching amplifier). The ES-150 guitar featured a single-coil, hexagonally shaped "bar" pickup, which was designed by Walt Fuller. It became known as the "Charlie Christian" pickup (named for the great jazz guitarist who was among the first to perform with the ES-150 guitar). The ES-150 achieved some popularity but suffered from unequal loudness across the six strings.
A functioning solid-body electric guitar was designed and built in 1940 by Les Paul from an Epiphone acoustic archtop. His "log guitar" —— a wood post with a neck attached and two hollow-body halves attached to the sides for appearance only — shares nothing in common for design or hardware with the solid-body Gibson Les Paul later introduced in 1952.
The feedback associated with amplified hollow-bodied electric guitars was understood long before Paul's "log" was created in 1940; Gage Brewer's Ro-Pat-In of 1932 had a top so heavily reinforced that it essentially functioned as a solid-body instrument. In 1945, Richard D. Bourgerie made an electric guitar pickup and amplifier for professional guitar player George Barnes. Bourgerie worked through World War II at Howard Radio Company, making electronic equipment for the American military. Barnes showed the result to Les Paul, who then arranged for Bourgerie to have one made for him.
Early proponents of the electric guitar on record include Alvino Rey (Phil Spitalney Orchestra), Les Paul (Fred Waring Orchestra), George Barnes (under many aliases), Eddie Durham, Lonnie Johnson, Floyd Smith, Big Bill Broonzy, T-Bone Walker, George Van Eps, Charlie Christian (Benny Goodman Orchestra), Tampa Red, Memphis Minnie, and Arthur Crudup. According to jazz historian James Lincoln Collier, Floyd Smith can be credited as the first person to rig up an amplified guitar. According to Collier, "Floyd's Guitar Blues" may be the first important use of the electric guitar on record.