Matheus Oliveira Diniz (born April 8, 1993)  is a Brazilian submission wrestler and Brazilian jiu-jitsu (BJJ) black belt competitor. His most notable achievement is winning the 2019 ADCC World Championship in the Middleweight division as well as being a medalist at the IBJJF World Championships in both Gi and No-Gi formats.
 Diniz was born on the 8th of April, 1993 in Uberlândia, State of Minas Gerais, Brazil. During his early years, his family moved to Formiga. When Diniz was 10, he started learning Capoeira, before switching in 2008 to Brazilian jiu-jitsu (BJJ) under coach Rodrigo Ranieri.
 After receiving his blue belt, Diniz moved to Poços de Caldas to train under Paulo Rezende who awarded him his purple and brown belts. As a purple belt Diniz won silver during the 2012 IBJJF World Championship in the medium heavy division. Diniz became acquainted with Marcelo Garcia who invited him to come to New York City to train at his academy. In April 2015, Garcia promoted Diniz to Black Belt.
 On September 16, 2018, Diniz faced Craig Jones at the main event of Grapplefest 2 that was held in Liverpool, UK. The match went to a decision with Jones winning by referee decision.
 Diniz competed at the 2019 ADCC World Championship in the middleweight division. He defeated Pedro Marinho, Gabriel Arges and Josh Hinger to reach the finals. In the finals, he defeated Craig Jones by winning on points to become champion.
 On October 2, 2020, Diniz was invited to compete in the main event of Who's Number One against Gordon Ryan. Diniz lost the match by submission, a heel hook. This match against Ryan was later awarded Match of the Year at the Jitsmagazine 2020 BJJ Awards. He was then invited to compete in the middleweight grand prix at BJJ Stars 4 on November 14, 2020. Diniz lost his opening round match against Otavio de Souza on advantages.
 On June 26, 2021, Diniz faced Lucas Barbosa at the co-main event of BJJ Stars 6. Towards the end of the match, as Barbosa was ahead on points, Diniz managed to lock his arm underneath Barbosa's chin. When the bell rang signalling the end of the match, Barbosa was left unconscious from the choke. After debate, it was determined that Barbosa went unconscious after the bell and therefore had won via points. The decision was considered controversial and attracted debate. He then competed in the main event of the inaugural Road to ADCC event on July 17, 2021, against Kaynan Duarte. He lost the match after being submitted with a heel hook.
 Diniz was invited to compete in the 88 kg division of the 2022 ADCC World Championship on September 17, 2022. He defeated Roberto Dib Frias 3–0 on points in the opening round before losing by submission to the eventual champion, Giancarlo Bodoni.
 Diniz competed at the IBJJF New York Open 2023 on August 5 and won gold in the ultra-heavyweight division. Diniz then won the no gi super-heavyweight division at the IBJJF Nashville Fall Open 2023 on November 12, 2023.
 List of achievements at black belt level:
 List of achievements in lower belts divisions:
 Mitsuyo "Count Koma" Maeda → Carlos Gracie Sr. → Helio Gracie → Rolls Gracie → Romero "Jacare" Cavalcanti → Fabio Gurgel → Marcelo Garcia → Matheus Diniz