According to Thefreedictionary.com, hard rock music is defined as "a style of rock 'n' roll characterized by a harsh, amplified sound and loud, distorted electric guitars." This style of music is a sub-genre of rock music and is usually highly amplified while being rhythmically simple.
Hard rock music generally uses heavy distorted electric guitars, bass guitars, keyboards and drums, with screaming (or intensifying) lead vocals. Generally, there are two types of guitarist in a hard rock band: the rhythm guitarist and the lead guitarist. The rhythm guitarist provides the chord changes and rhythm of the music (while accompanying the lead guitarist), as the lead guitarist plays the solos, riffs and fills of the music. The bassist and drummer will work together. The bassist outlines the harmony of the music while the drums produce and keep the rhythm.
Prior to hard rock music, blues and rock 'n' roll were the main styles of rock music. In the late 1960s, hard rock music became the "terminal point" of blues. At the time, blues had experienced white middle-class musicians attempt to reinvent music that had been developed by blacks. Hard rock music was based off of blues and rock 'n' roll, but was faster, louder and a stronger style of rock music that was more energetic than the style that blacks had created.
According to Scaruffi.com, the "apolitical" style of hard rock music had generated from progressive rock and rock 'n' roll bands including Free, featuring blues-rock vocalist Paul Rodgers, Status Quo, Thin Lizzy, UFO (who was into pop metal) and Uriah Heep (who wrote gothic and medieval music).
In the era of the development of hard rock music, there were numerous bands emerging and attempting to take the music a step further. Black Sabbath was a hard rock band that were known for their successful albums Paranoid (1970) and Master of Reality (1971), and for developing the vision of black metal and doom-metal rock. They did not create gothic music, but they became the first band to turn it into a genre. Queen were "the jokers of the hard-rock movement," according to Scaruffi.com. They combined their ideas of progressive-rock and gospel, and created a "bombastic" rock style that became famous after their hits "We Are The Champions" and "We Will Rock You."