Olajide Olayinka Williams "JJ" Olatunji, known globally by his online alias KSI, is a British multimedia powerhouse whose influence spans digital content, music, and sports entertainment. Born on June 19, 1993, in Watford, Hertfordshire, to parents of Yoruba heritage, he was privately educated at Berkhamsted School. His journey to becoming one of the United Kingdom's most recognizable personalities began in 2009 when he registered his YouTube channel, initially named KSIOlajidebt. He cultivated a massive following through energetic FIFA video game commentaries, later diversifying his content to include comedic vlogs and skits, which solidified his status as a pioneering online creator. By 2019, The Sunday Times ranked him as the second most influential online creator in the UK, a testament to his early digital dominance.

KSI's entrepreneurial spirit led him to co-found the YouTube collective the Sidemen, a group that became a cultural phenomenon in its own right. His business ventures expanded significantly with the co-founding of Misfits Boxing, a promotional company for influencer boxing events, and co-ownership of several successful brands, most notably the beverage company Prime Hydration with fellow influencer Logan Paul. His influence was further recognized by Forbes, which listed him in their 30 Under 30 Europe Entertainment list in 2021 and ranked him as the second-top creator of 2023. As of early 2025, his main YouTube channels boast over 44 million subscribers and 14 billion views.

Parallel to his online career, KSI forged a successful path in music. After early forays into hip-hop, he achieved his first commercial success with the 2015 single "Lamborghini" featuring P Money. His 2016 debut EP, Keep Up, reached number one on the UK R&B Albums Chart. His studio albums, 2020's Dissimulation and 2021's All Over the Place, peaked at number two and number one on the UK Albums Chart respectively, with the latter achieving a platinum certification. Hit singles like "Don't Play" with Anne-Marie and Digital Farm Animals and "Holiday" debuted at number two in the UK, earning Brit Award nominations for Song of the Year. In 2024, he received the Brit Billion Award for over one billion streams in the UK. His filmography includes the comedy Laid in America and the Amazon Prime Video documentary In Real Life.

In the boxing ring, KSI transitioned from online spectacle to legitimate competitor. His white-collar match against Joe Weller in 2018 and two high-profile bouts against Logan Paul—the second a professional match he won by split decision in 2019—catapulted influencer boxing into the mainstream. He continued fighting in 2022 and 2023, facing opponents including Swarmz, Luis Alcaraz Pineda, FaZe Temperrr, and Joe Fournier. His only professional loss came via unanimous decision against Tommy Fury in October 2023. Demonstrating his continued reach into traditional media, KSI joined the judging panel of Britain's Got Talent in 2026, marking a new chapter in his ever-evolving career as an entertainer and entrepreneur.