The latest season of Peaky Blinders has seen the Billy Boys loudly announce their arrival from Glasgow.
Series creator Steven Knight previously revealed that the Scottish hard men would appear alongside the fearsome Shelby family in the fifth run of the popular BBC drama.
And they took no time to acquaint themselves after sending a harrowing warning to the Tommy Shelby and the Peaky Blinders.
Who are the Billy Boys?
Based on the notorious razor gangs who ruled Glasgow's streets in the 1920s and 1930s, the gang have moved down south in the latest season of the show.
Glasgow's biggest razor gang was the infamous Bridgeton Billy Boys, led by Billy Fullerton, which boasted up to 800 members - it is believed that Jimmy McCavern's character is based on Billy.
The smartly dressed men, who looked like dead ringers for the Peaky Blinders themselves, would fashion knives, daggers and bayonets in the shipyards, which they concealed in hidden pockets.
The staunchly protestant gang was initially set up to fight against Irish immigrants but as well as the rampant sectarianism, the gang ran the entire neighbourhood, operating illegal scams, protection rackets and providing "stewards" for political meetings and open-air boxing bouts.
There were violent skirmishes with other gangs, often involving knives, hammers, broken bottles and chains.
Steven Knight, 58, previously told The Scotsman: "The truth is that in the late Twenties and Thirties really the hardest gangs were in Glasgow. There was a very definite structure to the gangs so I have been delving into the history of that.
"They become involved through a bit of invention, some creativity. We are going to start the series in 1929 which was a time of big economic upheaval and the gateway to the Thirties where we all know what happened. It’s a rich vein to be mining."
Speaking to the BBC, historian Dr Andrew Davies said: "There was a big problem with unemployment in Glasgow.
"In places like Calton and Bridgeton, thousands of young men were left with no job, no money and lots of spare time. This led to them hanging about on corners, getting drunk, stealing and resorting to violence. There was nothing else for them to do.
“Being in a gang, you wanted to be noticed and fashion played a big part in standing out. Gang members prided themselves on appearance, wearing suits and looking dapper. It was all part of their craving for recognition and status."
Who was their leader?
The gang took their orders from Billy Fullerton.
Former journalist Mr Jeffrey, who has written a number of books on Glasgow's gangs, told the BBC: "Like in gangster films and TV shows, such as Peaky Blinders, you needed someone at the top who has got to have the guts and the respect and carry the troops with him."
"It was so disciplined, it was like a private army."
According to the BBC, Fullerton's gang gave young men a sense of power at a time when many were unemployed.
The Billy Boys were anti-Catholic and often use to march through Irish immigrant areas of Glasgow in acts of intimidation.
They had a flute band and their own songs, including the infamous "Billy Boys", which was sung in the TV show - the song is often associated with supporters of Glasgow Rangers football club.
Mr Jeffrey added: "The main aim was to damage the Catholic population and make them feel unwelcome.
"They would march up and down Norman Street, where the Conks came from, and sing 'we are the Billy Boys'.
"The intention of that was to terrify the Catholic inhabitants of the area."
The activities of the gangs continued throughout the 1930s despite the crackdown from new police chief Percy Sillitoe, who waged war on their activities.
In the run-up to World War Two, Fullerton and the Billy Boys became involved with Oswald Mosley's fascists, providing a bodyguard for their meetings.
Fullerton died in 1962 at the age of 56.
Peaky Blinders airs on BBC One on Sundays at 9pm
