KSI and Logan Paul, YouTube stars with 37 million subscribers between them, will take their beef into the boxing ring in a fight billed as "the biggest event in internet history".

YouTubers around the world have chosen whose side they are on, and will be watching when the pair of social media heavyweights step into the ring at Manchester Arena.

Both are popular, divisive, and have highly controversial pasts.

Who are KSI and Logan Paul?

KSI is a 25-year-old British gamer, comedy vlogger and rapper whose videos have racked up 4.4 billion views despite heavy criticism for lewd comments towards women in some of his clips.

Photo: Supplied.

Logan Paul is the 23-year-old US prankster (and former state wrestler) who made his name on Vine before moving to YouTube, where he's had 3.9 billion views, and who caused outrage earlier this year for showing the body of an apparent suicide victim in Japan.

Both have cultivated a frenzied online feud in order to hype up this bout, which will be streamed pay-per-view on YouTube.

Their brothers Jake Paul (4.9b views) and Deji (3.3b) will fight on the undercard.

A chance for redemption?

Both seem to have shrugged off their controversies, but the fight will be seen by some as a way to prop up, and cash in on, their careers.

Asked by BBC News whether he's hoping to redeem himself, Logan said: "I don't think this is the redemption. I think it may mark a part of it, but by no means is this fight a redemption for my mistake that happened in January.

"But I think it is an opportunity to for me to have taken a step back from the internet and focus my efforts elsewhere, and it's an opportunity for me to show the world a new version of Logan Paul, not just silly internet vlog boy."

Photo: AFP

Of past behaviour, KSI, or Olajide William "JJ" Olatunji Jr, said: "I definitely have regrets for some of the things I've said and done, but you know, I'm a human being and human beings make mistakes."

What the fans are saying

At one of KSI's training sessions in Manchester before the fight, fan Shaf Miah, 25, from London, said the white-collar amateur bout was "the next level of internet beef".

"If you read comments [on YouTube], people want to physically hit someone if they don't like them or if they've done something annoying. And to see their favourite YouTuber do it for them, they're obviously going to pay money to watch it."

Michael Zepeda, 21, who arrived from LA for the fight, said: "They've both got a lot of subscribers, they both get a lot of views," he said.

"Everybody wants to watch. I want to see Logan get his ass beat. He deserves it. He's done many messed up things for views. He crossed that line, definitely."

CJ Melia, 21, has travelled to Manchester from Dublin. "I cannot wait," he said.

"I'm so excited for this. I've been watching KSI for about nine years. He's the reason I started my first YouTube channel eight years ago."

How the bout came about

This all started when two other YouTubers - Joe Weller and Malfoy - went into the ring last year, and KSI said he would fight the winner.

KSI took on Mr Weller at the Copper Box Arena in London in February, and won. That was streamed live on YouTube for free, with 1.8 million people watching live and 36 million more watching on the pair's official channels since.

Mr Weller has five million subscribers to Logan Paul's 18 million. Saturday's fight will be much bigger - but this time, punters have to pay £7.50 ($NZ14.42) to watch.

The biggest event in internet history?

The Duke and Duchess of Cambridge might have something to say about that. Their 2011 wedding holds the Guinness World Record for the most live streams for a single event, at 72 million - although that was not a product of the online world, as this fight is.

YouTuber Jordan Antle said the fight's billing was not over the top.

"This is a massive event and I would definitely say this is going to be one of the biggest internet events so far in history.

"Seeing two YouTubers who have a large fanbase fighting each other live in front of millions of people in unheard of. It's a very strange combination of two worlds and it's attracting a lot of attention because of how different it is."

KSI and the Paul brothers have done their best to attract interest.

Insult-filled videos and diss tracks have flown back and forth, and ill-tempered press conferences have taken place in Los Angeles and London.

- BBC