The first electric bass was invented in 1930 in Seattle, Washington, by Paul Tutmarc, who was also a musician. He sold his "electronic bass fiddle" in his company's catalog "Audiovox." 
The electric bass looks much the same as an electric guitar except:
1. The neck is longer
(because longer strings produce lower tones)
2. Usually the bass has four strings instead of 6
(some have more than 4 strings)
The four strings of a bass guitar are tuned to same pitches as the four lower strings of the regular guitar, E, A, D, G. The electric bass must be plugged into some sort of speaker for the electronic amplification of its sound.
The bass guitar was designed to replace the double bass (see image, right), which is a rather large instrument and a difficult instrument to haul around. The bass guitar was specifically developed to be a more portable instrument, especially in the context of a touring band.
As with the double bass, the electric bass is considered a "transposing" instrument, because the bass clef notation used in music that the bass player reads is played an octave lower than written (hence the name "double bass.") This is to avoid the use of ledger lines.
String are generally all-metal strings and include roundwound, flatwound, groundwound or halfwound.
The most common wood for a bass guitar is alder for the body, maple for the neck and rosewood for the fretboard. Mahogany, ebony and poplar are also used.
The electric bass is part of the rhythm section of the band along with the drummer, not only helping to keep the beat and but also to keep the harmonic foundation intact.
It wasn't until 1951, however, that Leo Fender and George Fullerton unveiled the Fender Precision Bass. This new instrument was successful and in fact, became widely copied by other companies. A notable first user of the Fender Bass was Bill Black, who traveled with Elvis Presley.