Casimiro de Nascimento Martins, better known as Rei Zulu (born 9 June 1947), is a Brazilian retired vale-tudo fighter who specialized in tarracá, a traditional fighting style from his native Maranhão.

In 1980, after 17 years of competition, his career had initially ended after approximately 150 fights after being caught in a guillotine move by Euclides Pereira.

The undefeated Rickson Gracie fought Rei Zulu, who had to that point a 170–0 record and was alleged to have had up to 270 wins in the vale tudo circuit, in a televised fight that was historic for the development of the Brazilian MMA scene.

However, on 30 November 1984, he had his most major victory against competitor Sérgio Batarelli, a kickboxing fighter, during the JJ vs MA-Jiu-Jitsu vs Martial Arts event.

[8] On 6 April 2000, in the state of Piauí, in a televised fight, Rei Zulu, at 55 years old, lost to kung fu fighter Wellington Dourado.