They all grew up in west London, and all wound up in the same cell of the Islamic State group guarding, torturing and killing hostages in Syria and Iraq.
Now, the last two members of the group dubbed the "Beatles" by their hostages, Alexanda Kotey and El Shafee Elsheikh, have been arrested by Syrian Kurdish fighters.
The group of four British men were radicalised in the UK before travelling to Syria, where they became infamous for their high-profile executions of Western hostages.
US officials believe the "execution cell" beheaded more than 27 Western hostages and tortured many more.
Each was known to their hostages by their respective Beatles moniker - Paul, Ringo, John and George.
Spanish journalist and former hostage Javier Espinosa, told the BBC in 2017 that the group were "thugs with no knowledge of what is religion at all".
But who were the IS "Beatles"?
Mohammed Emwazi, dubbed Jihadi John in the media, fronted a number of IS propaganda videos where Western hostages were shown executed.
Born in Kuwait, his family moved to the UK when he was six years old in 1988. He was educated in north London, and graduated from the University of Westminster in 2009 in computer programming.
While in the UK, he came under surveillance from UK intelligence services after travelling to Tanzania and Kuwait. He was linked with a number of high-profile suspected jihadists that MI5 were tracking.
His family reported him missing in 2013. Throughout 2014 he appeared in number of videos, with his face disguised, where Western hostages including US journalist James Foley and UK aid workers David Haines and Alan Henning appeared to be beheaded.
The last known video appearance from him was January 2015. A top target for intelligence services, he was killed in a US drone strike on 12 November that year.
Aine Davis was arrested near Istanbul in 2015, and convicted in Turkey in 2017 of being a senior member of a terrorist organisation.
Back in London he had lived in Hammersmith. He had a number of drug convictions and was jailed in 2006 for possessing a firearm.
After converting to Islam, he changed his name to Hamza and met Emwazi. The two were part of a group that radicalised Muslims living in London. He left the UK to join the IS in 2013.
After being arrested he denied being part of the terror group, or "the Beatles" cell.
Alexanda Kotey is of Ghanaian and Greek Cypriot background, and attended the same al-Manaar mosque in west London as Emwazi.
He was described by neighbours as "quiet and humble" and a dedicated fan of the Queens Park Rangers football team, the Buzzfeed news website reported.
He was identified as one of the gang by the US state department, which said he was likely to have been a recruiter of UK nationals to the group.
US officials have said that he and fourth member El Shafee Elsheikh were captured by members of the US-backed Syrian Democratic Forces (SDF), who are targeting remnants of IS.
Both Elsheikh and Kotey are designated as terrorists by the US state department, who link them to the group's executions and "exceptionally cruel torture methods" including electric shocks, waterboarding and mock executions.
The son of Sudanese refugees, Elsheikh went to Syria in 2012 and joined al-Qaeda there before aligning himself with IS, the New York Times reports.
The men were said to have been detained in mid-January after Kurdish fighters suspected they were foreign fighters. Their identities are reported to have been confirmed by the US using biometric testing including fingerprints.
News of their arrest emerged initially in US media, before being confirmed by officials.
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