Final answer:
Jerry Lee Lewis was the star from Louisiana signed by Sam Phillips who initially rivaled Elvis' popularity, known for blending various Southern music traditions into early rock and roll.
Step-by-step explanation:
After Elvis Presley's contract was sold to RCA Records by Sam Phillips of Sun Records, a label that also signed Johnny Cash and Carl Perkins among others, the star from Louisiana who initially rivaled Elvis' popularity was Jerry Lee Lewis. He like Elvis, was deeply influenced by African American music and childhood experiences with various musical genres.
Jerry Lee Lewis' dynamic piano playing and wild stage antics helped propel his fame, with hits such as "Great Balls of Fire" and "Whole Lotta Shakin' Goin' On", making him an iconic figure in rock and roll history. Like other Sun Records artists, he blended country, rhythm and blues, and other Southern music traditions to create the early rock and roll sound.