From an Old School Hip Hop site
Rap music has always existed as an element of Hip Hop since the culture's birth in the early 1970s. The first rappers (called MCs) would rap over funk, reggae, dub, soul, and disco beats and would hold spontaneous rhyming battles that were meant to verbally attack an opponent called "freestyles" (freestyling and flowing were words used to describe the impromptu vocal delivery). Artists that laid the template for such aggressive spoken word set to a funky beat include James Brown, Gil Scott-Heron, The Watts Prophets, and The Last Poets.
By the spring of 1979, the first rap record surfaced with funk band The Fatback Band's "King Tim III (Personality Jock)". Later, The Sugar Hill Gang debuted in the summer with Hip Hop's most famous commercial record yet,"Rapper's Delight".