Diogo Reis was born on March 20, 2002, in Manaus, Amazonas, Brazil — a city that has proven to be fertile ground for world-class grappling talent. His introduction to jiu-jitsu came at age 10, sparked by his older brother's enthusiasm for the sport. That early influence planted a seed that would grow into one of the most decorated careers of his generation. Reis took his first steps on the mats under coach Alexandre Oliveira, building the technical foundation that would accelerate his rise through the ranks. His Manaus roots remain a central part of his identity, and the competitive hunger forged in the Amazon has followed him to every major grappling stage in the world.

Long before competing as a black belt, Diogo Reis announced himself as a generational prodigy by sweeping all four major IBJJF tournaments at the juvenile and colored belt levels — the World Championship, Pan Championship, Brazilian Nationals, and European Open. This clean sweep of what is commonly known as the Grand Slam of Jiu-Jitsu is an exceptionally rare achievement, and it foreshadowed the elite success that would define his adult career.

Reis began accumulating national titles as early as 2015, claiming gold at the CBJJ Brazilian Nationals in the teen division, with further teen national titles following in 2016. By 2017, he had extended his reach to the international stage, winning both the IBJJF Pan Kids Championship and the IBJJF American Nationals in the teen category. His juvenile career peaked across 2018 and 2019, when he secured back-to-back IBJJF Juvenile World Championship titles alongside victories at the 2019 IBJJF Pan Championship, the 2019 IBJJF European Open, and the CBJJ Brazilian Nationals Juvenile. At every age group and belt level he entered, Reis demonstrated a consistency that marked him as something far beyond a typical young prospect.

Diogo Reis earned his black belt on December 13, 2020, under Melqui Galvão — a promotion that came when Reis was just 18 years old, representing an unusually compressed timeline from prodigy to the sport's highest rank. In a detail that speaks volumes about his competitive hunger, his black belt debut actually preceded the formal ceremony by one week: on December 6, 2020, Reis stepped onto the AJP Tour Grand Slam competition floor in Rio de Janeiro and earned a silver medal, competing at the black belt level before the promotion had even taken place.

His development within Melqui Galvão Jiu-Jitsu placed him alongside teammates such as Mica Galvão and Fabricio Andrey, forming part of a powerhouse Manaus squad that drew significant attention on the international circuit. In 2022, the team aligned with Fight Sports to expand their international exposure and access to major competitions. By early 2023, Melqui Galvão had parted from that partnership to establish an independent association, and Reis remained a central figure of the revived Melqui Galvão Jiu-Jitsu team — carrying the competitive flag for his hometown organization on the world stage.

His early black belt years produced a string of high-level results, including victories at multiple AJP Grand Slam events and the AJP Abu Dhabi World Pro in 2021, establishing him as one of the most dangerous competitors in the sport's lighter weight divisions before he had even turned 20.

The defining chapter of Diogo Reis's competitive career arrived at the 2022 ADCC World Championship, where he claimed gold in the 66 kg division and announced himself at the absolute highest level of no-gi grappling. That victory was more than a singular achievement — it was the beginning of a reign. Two years later, at the 2024 ADCC World Championship, Reis returned to the 66 kg bracket and defended his title, becoming a back-to-back ADCC champion in one of submission grappling's most fiercely contested divisions.

The path to that second title was not without adversity. A knee injury sustained in a match against an opponent known as "Pato" forced Reis to withdraw from a scheduled ONE Championship appearance against Mikey Musumeci. Rather than rush his return, he chose conservative treatment and committed to six months of physical therapy, focusing on building muscle mass to stabilize the injured joint. He kept Musumeci's team informed throughout his unavailability and used two ADCC matches during his recovery as structured performance benchmarks — a methodical approach that underscored the discipline behind his championship preparation. Throughout 2024, Reis concentrated exclusively on no-gi competition to give the ADCC title defense his full focus, and that commitment was rewarded with gold.

The back-to-back titles cement Reis's status as one of the defining grapplers of his generation at 66 kg, and his ability to navigate injury and recovery without compromising his standards reflects the mentality that has driven his career from its earliest days in Manaus.

In 2024, Diogo Reis expanded his competitive footprint by signing with ONE Championship, bringing his submission grappling to one of the world's most prominent combat sports platforms. The move represented a strategic step beyond the traditional tournament circuit, placing him in front of a global mainstream audience. His promotional debut came at ONE Fight Night 29 on March 7, 2025, where he faced Shoya Ishiguro in a submission grappling bout and delivered an impressive performance, validating his standing among the sport's elite in an international broadcast setting.

Later in 2025, Reis returned to compete for the ONE Flyweight Submission Grappling World Championship at 61 kilograms, facing Daiki Yonekura at ONE Fight Night 38 on December 5, 2025. He won the title, adding a ONE Championship world title to his ADCC gold medals and completing a remarkable year of competition. On January 2, 2026, ONE Championship named Reis their Submission Grappler of the Year for 2025, recognizing the totality of his performances across the promotion.

Throughout this period, Reis received outreach from the UFC but remained committed to his existing ONE Championship obligations — a decision that reflects the value he places on honoring professional contracts and continuing to build within the ecosystem he joined. His presence on the ONE platform has meaningfully broadened his personal brand and brought professional jiu-jitsu to a fanbase far beyond the traditional grappling community.

Diogo Reis earned the nickname "Baby Shark" as a reflection of both his rapid ascent and the relentlessly aggressive manner in which he competes. His game is built on high-pressure wrestling and constant submission hunting — a combination that keeps opponents perpetually on the defensive and manufactures danger from virtually any position. He does not wait for opportunities; he creates them through physicality, pace, and positional awareness that belies his age.

Reis competes primarily at rooster and light-featherweight in the gi, but has pursued featherweight matchups as a deliberate choice to seek tougher competition and test himself against larger opponents. This willingness to step outside favorable matchups in search of greater challenge is a recurring theme throughout his career. Weight management adds another layer to his competitive profile — maintaining strength while cutting to 61 kilograms for ONE Championship competition presents a genuine physiological challenge he has navigated carefully as part of his preparation.

The combination of elite credentials across both gi and no-gi formats, a submission-first mentality, and a readiness to pursue difficult matchups makes Reis a dynamic and unpredictable presence in any bracket he enters.

Beyond his athletic career, Diogo Reis fulfilled a deeply personal ambition in 2023 when he was officially inducted into the Brazilian Army as a Third Sergeant. He attained the role through a special program designed for high-performance athletes, which allows competitors of national standing to serve while maintaining their training and competition schedules. For Reis, the induction was the realization of a childhood dream — wearing the army uniform had long been a personal aspiration, and achieving it at the peak of his athletic career gave the accomplishment particular significance.

Reis frames his dual role as representing Brazil in two distinct arenas: on the competition mats at the highest levels of international grappling, and in uniform as a member of the country's armed forces. The discipline, structure, and sense of national pride embedded in military life align naturally with the dedication required to compete at the ADCC and ONE Championship levels. Reis speaks about these commitments as complementary rather than competing obligations — each reinforcing the standards he holds in the other.

Looking beyond his submission grappling career, Diogo Reis has taken concrete steps toward a potential transition to mixed martial arts. He trains his striking at the Fighting Nerds gym, developing the stand-up skills that would complement his elite grappling foundation in an MMA context. Rather than relying solely on grappling to carry him in MMA, Reis builds a well-rounded skill set that professional competition at that level demands — a strategic and deliberate approach consistent with how he has approached every stage of his career.

As of early 2026, Reis has not made a professional MMA debut, and his record in that discipline stands at 0-0-0. His appearances under the ONE Championship banner — including his debut against Shoya Ishiguro at ONE Fight Night 29 — have been submission grappling bouts, distinct from MMA competition. The striking development underway, combined with grappling credentials that include back-to-back ADCC titles and a ONE Championship flyweight submission grappling title, positions Reis as a credible future MMA prospect whenever he chooses to make that transition.