Rex Robert Brown (born July 27, 1964) is an American musician and songwriter, best known as the longtime bassist for heavy metal band Pantera (1982–2003). He is a former member of Down (2001–2011) and the former bassist for the band Kill Devil Hill. He released his debut solo album Smoke on This… in 2017. For the first time in Brown's career, the work features him not only as a bassist but also as lead vocalist and guitarist. Brown authored a book called Official Truth 101 Proof, which was released in April 2013. The book documents Pantera's formation, career, and disbandment.

Rex Robert Brown was born in Graham, Texas, on July 27, 1964. His father was forty when Brown was born, and died in 1971. He was raised by his mother and sister. Brown was first introduced to music through his grandmother, who taught him to play the piano when he was a child, and turned him onto ragtime music and Scott Joplin. Brown was a member of the Boy Scouts of America and achieved the rank of Eagle Scout. Brown became a fan of ZZ Top and Def Leppard as a youth, and started playing bass when he was twelve years old. He remains a fan of Black Sabbath, Led Zeppelin, and hardcore punk.

Pantera was formed in 1981. Brown joined Pantera on bass in 1982 replacing Tommy D. Bradford and adopting the alias "Rex Rocker". Brown was a classmate of, and played in the high school jazz band with, drummer Vinnie Paul, and guitarist Dimebag Darrell (then known as Diamond Darrell). Brown was credited as "Rex Rocker" on Pantera's first three albums: Metal Magic (1983), Projects in the Jungle (1984), and I Am the Night (1985), he would be credited by his birth name starting with the band's fourth album Power Metal and onwards.