The origin of guitar-like instruments is uncertain, but the first documented instruments of this kind are the lute, the Spanish vihuela, the Arabian 'ud, the Romanian cobza and the mandolin. The oldest one is the 'ud, that was probably invented at about the 3rd century. It had five strings made of gut, but the number of strings and the shape of the instrument vary according to place and time. The vihuela, from the 16th century, had six double courses of strings. The lute was invented circa 1500 and was used a lot on the next centuries. It had six pairs of strings (sometimes the highest one was single).  On the Baroque era, lutes with additional bass strings were built. The guitar, as we know today, was developed in the 19th century, with its shape and machine heads instead of tuning pegs. Other varities appeared, as the 12-string guitar and the Hawaiian guitar, or steel guitar. On the 1930's, the Electric Guitar was invented, and was developing itself due to names like Les Paul, who created the first solid-body electric guitars, Leo Fender, who made one of the most traditional guitar enterprises, and Seymour Duncan, the most famous guitar pickup creator. Fender invented the Broadcaster, later renamed Telecaster, the first success of the company. Then, on the 50's, the legendary Fender Stratocaster was invented and then Gibson made the Gibson Les Paul. Other  guitars were made famous, as the Gibson SG, the Flying V, the Explorer, the Rickenbackers, Gretschs and many others. An important modification on the electric guitar was the use of the tremolo arm or "whammy bar", a device used to bend the notes downwards. Lots of types of bridges with tremolo arms were made, and the most famous is probably the Floyd Rose. There were others like the Kahler and the one developed with the Steinberger guitars, that have the machine heads on the body instead of the neck. As the electric guitar can be made in any shape, because its body can be nonresonant, there's a wide variety of guitar shapes nowadays. The guitar is probably the most popular musical instrument in the present, with players all around the world.