His parents initially disapproved, but later became supportive and featured in a number of his videos. He registered his current YouTube account on 24 July 2009 under the name KSI Olajide BT, where he uploaded gaming–commentary videos of the FIFA video game series from his bedroom at his parents' house in Watford. The brothers ranked first and second respectively as the "UK's Most Influential YouTube Creators" by Tubular Labs in 2015. In 2023, he fought FaZe Temperrr in January, Joe Fournier in May, and Tommy Fury in October, which he lost via unanimous decision. He received the Brit Billion Award in 2024, for amassing over one billion music streams in the United Kingdom. In 2021, he was listed in the Europe Entertainment category of Forbes 30 Under 30; he was later ranked by Forbes as the second-top creator of 2023.

The album spawned two further UK top 40 singles, "Cap", featuring Offset, and "Killa Killa", featuring Aiyana-Lee. The album debuted at number two on the ksi online game UK Albums Chart and further charted in 15 other countries. The song peaked at number 10 on the UK Singles Chart and it has been certified silver by the British Phonographic Industry (BPI) for sales of 200,000 units in the country. It was performed live by the three featured artists as KSI's entrance music for his boxing rematch against Logan Paul. On 8 November 2019, "Down Like That", featuring Rick Ross, Lil Baby and S-X, was released as the album's lead single.

Other popular videos include a "Sidemen Tinder" dating series, eating challenges and comedy roasts. Following Bruno Tonioli’s decision to leave Britain’s Got Talent, musician, YouTuber, and boxer KSI has been announced as a full-time judge. Theroux stated that it would be "an opportunity to see another side of JJ, understanding how he got where he is, the world of a premium online content creator today, and a man who has made it his brand never to lose, as he takes on the music business." The film reveals the behind-the-scenes story of what led KSI to become the YouTube champion of the world after his boxing debut fight against fellow YouTube star Joe Weller and how KSI will use what he learned to fight Logan Paul. Jason Best of Movie Talk gave the film 1 out of 5 and called it "Crass and witless."

Starting Influencer Boxing Against Joe Weller

On 4 November 2019, it was announced that KSI had signed with RBC Records and BMG to "take his music to the next level" and "further develop his music career in the US and internationally". It debuted at number 17 on the UK Albums Chart and at number one on the UK R&B Albums Chart. On 12 April 2019, KSI released a collaborative album with Randolph titled New Age. KSI released "On Point" on 17 August 2018, which was played during his ring walk for his second boxing bout. One week before its release, KSI announced that the EP would be his "final release" with Island Records and that he would be releasing music independently. The EP's second single, "Friends with Benefits", featuring MNDM, was released on 29 July 2016, reaching number 69 on the UK Singles Chart. The song charted at number 30 on the UK Singles Chart, and remained on the charts for another two weeks, moving to number 68 and then to number 96 before dropping out of the top 100.

2020: New Record Label Signing And Dissimulation

"We built something that none of us ever thought was possible especially back then when we were making random videos together and playing GTA," he said, referring to Grand Theft Auto. "But after a lot of thought, I've decided that I will no longer be doing Sidemen videos. Today, 31 May, will be my final Sidemen video." "I've gone back and forth on this decision for a very long time," he added. The newest series of Britain’s Got Talent will certainly have a different feel with the inclusion of KSI, who boasts a huge online following. In the years since, KSI has gone on to collaborate with major artists as well as performing at major music venues. KSI, whose real name is Olajide Olayinka Williams Olatunj, is often called ‘JJ’ by his friends and fans. But, to find out more about BGT’s newest YouTuber-turned-boxer, Metro has taken a deeper look into his background. On 17 August 2024, KSI, along with the Sidemen, appeared and was ranked 21st on The Times's list of "The UK’s top 30 richest gamers and creators in 2024", estimating £50 million in fortune shared among the group.

After the bout had concluded, KSI lashed out at Fury and insisted that the result was a "robbery." Many online and attendees sided with KSI, bevelling that he did enough to win the fight, including English sports promoter Eddie Hearn, who was in attendance. On 15 May, Fournier appealed the decision, and the Professional Boxing Association (PBA) called for both fighters to make their cases, and a decision will be made by 19 May at the latest. KSI defeated Paul via split decision, with two judges scoring the bout 56–55 and 57–54 in favour of KSI, and a third judge scoring the fight 56–55 in favour of Paul. One of the EP's songs, "Touch Down", featuring rapper and singer Stefflon Don, appeared on the soundtrack of the 2017 film Baywatch. KSI started making videos in 2008 and rose to fame as an online streamer.

Forbes reported that KSI was contracted to earn a minimum amount of $900,000 from his second fight against Logan Paul in 2019. Some estimates calculated the potential earnings at £30 million to £40 million from each fight, but KSI dismissed these claims, stating that his earnings were "a high amount" but "nowhere near £40 million or £20 million". On 6 March, Variety announced that KSI alongside After Party Studios will be producing a docuseries titled "Race to the Top", chronicling his takeover of the club similarly to "Welcome to Wrexham." In June 2021, KSI announced that he and Wasserman Boxing had partnered up to launch a boxing promotional company called 'Misfits Boxing'. In February 2021, KSI announced on Twitter the creation of his own record label named "The Online Takeover" in partnership with his music manager Mams Taylor. KSI and the Sidemen have founded multiple businesses throughout their online careers.

The song received a positive reception following the negative response to "Thick of It". On 19 November, KSI received BRIT Billion Award for amassing over one billion music streams in the UK. On 3 October, KSI released both songs as a double-single release, the latter of which was subjected to negative reception and mockery. The song peaked at number three on the UK Singles Chart and became one of the UK's best-selling songs of 2020. KSI was scheduled to perform at Parklife, Longitude and Reading and Leeds music festivals in 2020 to promote Dissimulation, but these were later cancelled due to the COVID-19 pandemic.

Sam Neill's Tearful The Assembly Interview Is One Of Tv's Most Beautiful Moments

"Keep Up", the title song for KSI's debut extended play of the same name, featuring Jme, was released on 13 November 2015, reaching number 45 on the UK Singles Chart. The group produces online videos, most often consisting of challenges, sketches and video-game commentary, as well as selling exclusive Sidemen merchandise. Two further boxing events against American YouTuber Logan Paul took place, the second of which was a professional bout in which he won via split decision in November 2019. Creating hip-hop music as early as 2011, he first achieved commercial success with "Lamborghini" (featuring P Money) in 2015. In 2019, he was ranked second by The Sunday Times in its list of most influential online creators in the United Kingdom. He is also a musician, former boxer and recently bought a minority stake in Dagenham & Redbridge Football Club.

In July 2024, KSI appeared in a YouTube video challenge by American YouTuber MrBeast titled "50 YouTubers Fight for $1,000,000". In September 2023, Forbes ranked KSI as the second top creator of 2023, earning an estimated $24 million. In 2019, he was ranked second by The Sunday Times in its list of the top 100 UK influencers. Shortly thereafter, he released a number of diss track videos criticising members of his then-former group, to which most of the members responded back with their own. A year later in November 2016, he was ranked first on Business Insider's list of "The 19 biggest British YouTube stars". In September 2015, KSI was ranked 15th on Business Insider's list of "The 15 most popular YouTubers in the world". On 18 August 2014, KSI teamed up with Endemol for a new sports show called Rule'm Sports.

In 2016, KSI and Caspar Lee starred in the British direct-to-video comedy film Laid in America. On 15 October, the results were changed to a unanimous decision victory for Fury due to judge Rafael Ramos, who had previously scored the bout on the scorecard, which was mathematically incorrect. On 15 December KSI, Miniminter, TBJZL, and Zerkaa released a Christmas themed single titled "The Gift" under the Sidemen banner featuring S-X which charted at number 77 in the UK. The song played during KSI's ring walk for his boxing fight against Joe Weller and charted at number 89 on the UK Singles Chart. On 29 April 2016, KSI released "Goes Off", featuring Mista Silva, as the first single from his second EP titled Jump Around.

In that video, KSI also confirmed he will be fighting on 31 August 2024, in Dublin, Ireland, and challenged American internet personality Slim Albaher and American mixed martial artist Anthony Taylor to a 2 vs. 1 outnumbered tag team match. Unlike the first fight, the rematch was a professional fight without the use of headgear. The fight ended as a majority draw, with two judges scoring the fight even at 57–57 and a third judge scoring 58–57 in favour of KSI. On 24 February 2018, it was announced that KSI would be fighting Logan Paul in a white-collar boxing amateur boxing match. The fight was won by KSI 1 minute and 37 seconds into the third round by way of technical knockout. On 30 May, KSI released another double-single with "Catch Me If You Can" and "So Far Away", the latter featuring S-X which had previously leaked in July 2024 alongside "Dirty".

In June 2024, KSI alongside the Sidemen created a reality competition series called Inside. The film was produced by fellow YouTuber Callux's film studio, After Party Studios, and was distributed by Sony Pictures Home Entertainment. The film was released direct-to-video by Universal Pictures on 26 September 2016. The film was written and directed by Sam Milman and Peter Vass and was produced by The Fun Group LLC and Max Gottlieb. On 10 January 2026, in an interview with Ranveer Allahbadia, KSI announced his retirement from boxing, stating that he was “done with boxing” and had even turned down deals to fight Jake Paul that were up to $30 million. However, fans began to speculate if the bout had been cancelled following KSI deleting the bout announcement across his social media.

He registered the YouTube channel KSIOlajidebt in 2009 and built a following through his commentary videos of the FIFA video game series. Olajide Olayinka Williams "JJ" Olatunjic (pronunciationⓘ born 19 June 1993), known professionally as KSI,d is a British influencer, musician, and former professional boxer.