Gesias Cavalcante Souza (born July 6, 1983) is a Brazilian professional mixed martial artist. He is the 2006 and 2007 K-1 HERO'S Middleweight tournament champion. He is billed as "JZ Calvan" in Japan.

While Cavalcante is primarily an MMA fighter, he made his K-1 debut fighting against Masato in the 2007 World Max tournament, losing via decision. He currently trains with American Top Team.

On September 17, 2007, Cavalcante won the K-1 HERO'S' 2007 Middleweight (70 kg) tournament by defeating Brazilian jiu-jitsu specialist Vitor Ribeiro by TKO in the first round and Andre "Dida" Amade by submission via armbar in the finals.

Cavalcante had agreed to fight former PRIDE Fighting Championship lightweight standout Shinya Aoki at Yarennoka! but withdrew from the fight due to a knee ligament injury. The match was rescheduled for March 15, 2008 at DREAM.1 to kick off the new DREAM promotion at Saitama Super Arena.

Early in the first round, the referee stopped the action when Cavalcante apparently landed illegal elbow strikes to the back of Aoki's neck. The ringside doctor announced that Aoki was unable to continue due to the injury and Cavalcante apologized for the incident. The fight resulted in a no contest. Elbow strikes to the neck and spine area are illegal under DREAM rules. Aoki was later found to have sustained concussion of the cervical vertebra.

They had their rematch on April 29, 2008 at DREAM.2. In that match, Aoki defeated Cavalcante via unanimous decision. However, he sustained a severely bruised rib and tore cartilage in his costal area during the match.

Cavalcante's next fight was set to be against Joachim Hansen at Dynamite!! 2008 on December 31, 2008, but the bout was canceled the day of the event due to Hansen not passing pre-fight medicals and subsequently being hospitalized for a "head injury".