https://www.theguardian.com/uk-news/2018/jul/23/uk-will-not-oppose-us-death-penalty-for-isis-beatles

"The Beatles", dubbed as such by their hostages because of their English accents, was an Islamic State of Iraq and the Levant (ISIL) militant group. Its members were nicknamed "John", "Paul", "George", and "Ringo" by the hostages, after the four members of the British rock group the Beatles. In November 2015, one of the militants was killed and one was arrested, and the final two were caught in early 2018.

They are responsible for beheadings in Iraq and Syria, most notably as shown in the beheading videos of American journalists James Foley and Steven Sotloff, and British aid workers David Haines and Alan Henning, in 2014..

https://en.wikipedia.org/wiki/The_Beatles_(terrorist_cell)