Hailed as one of the show's biggest villains to date, the character was an East End crime boss who quickly emerged as the new gangland kingpin of Albert Square.

The character's story arc begins with Johnny usurping fellow mob boss Andy Hunter (Michael Higgs) from his position as the square's reigning crime kingpin.

Soon afterward, Johnny forces the local Ferreira family out of Walford before establishing an unlikely friendship with his old acquaintance Pat Butcher (Pam St Clement).

He also destroys his own relationship with former mistress Tina Stewart (Charlotte Avery); hired Peggy's nephew Billy (Perry Fenwick) to become Danny's replacement until he later fires him for conspiring with his family; developed a conflict with Ruby's best friend, Stacey Slater (Lacey Turner), over the way her rebellious friendship strains his daughter's education; blackmailed Danny's brother Jake (Joel Beckett) with the discovery that his girlfriend Chrissie Watts (Tracy-Ann Oberman) murdered her estranged husband Den (Leslie Grantham) and framed Peggy's daughter Sam (Kim Medcalf) for the crime; constantly tormented Ruby's boyfriend Juley Smith (Joseph Kpobie) upon learning that he is the reason she lost her virginity to him; and arranged for popular hard man Dennis Rickman (Nigel Harman) to be fatally stabbed on New Year's Eve 2005; after being attacked by the latter in retaliation for threatening his adoptive sister-turned-recent wife Sharon (Letitia Dean).

In October 2006, nearly seven months after being sentenced to life imprisonment for his gangland activities, the characters story arc ended with Johnny being axed from the programme.

His last appearance was screened during Ruby's eighteenth birthday, wherein Johnny attempted to perpetuate the death of Stacey's brother Sean (Robert Kazinsky) after finding out that he has been forging a romantic business partnership with Ruby to extract control of both her financial welfare and family assets; however, this failed when Johnny ended up having a fatal heart attack in prison, and he dies in hospital off-screen.

Johnny Allen makes his first appearance on 4 January 2005, when he arrives in Albert Square — the community of Walford, a fictionalized area of East London — to confront his henchmen, Jake Moon (Joel Beckett) and brother Danny (Jake Maskall), for having a problem with his package job; namely to deliver a duffel bag of money to one of his 'mates' in Walford's residential community, Albert Square.

When Johnny inspects the bag that Jake and Danny had, he uncovers hidden cocaine and — sensing the problem behind his plan — orders the brothers to remain in the square under further notice.

He arranges for the two to stay with their cousin Alfie (Shane Richie) and later has them work for their enemy and the square's reigning crime boss, Andy Hunter (Michael Higgs).

In doing so, Johnny further deteriorates Andy's public image in the community and proceeds to establish support from many of the Walford residents — including Patrick and his wife, Yolande (Angela Wynter).

Outraged over his humiliation, Andy vows to get revenge on Johnny and hatches a plan to take his £750,000 in their upcoming transaction and flee Walford with the money.

The conversation seemingly ends with the pair going separate ways, as Johnny offers Andy a handshake before giving him 'one final tip.'

Johnny later recruits Sam's cousin Billy (Perry Fenwick) to replace the Moon brothers and even steals Danny's idea for a salsa night at the club.

Peggy also has knowledge of Johnny's past crimes, such as cutting the fingers off the hand of a prostitute named Suzy Laura and brutally beating up his old friend Dougie Collins (David Simeon) for a slight misspelling on a birthday cake.

Ruby walks into the pub as the story unravels and soon begins to learn of her father's true past — including that he may be to blame for the deaths of her mother and sister.

Johnny's feud with Peggy continues as she appears to turn his daughter against him, up to the point where Ruby confides to her best friend, Stacey Slater (Lacey Turner) about this, and the pair later inform Tina about his behavior.

She is nearly attacked until Billy arrives with her two sons, Phil (Steve McFadden) and Grant (Ross Kemp), who rescue their mother by knocking out Sean.

The Mitchell brothers learn that Johnny organized the mugging and plan to confront him despite Peggy's reservations, up to the point where she and Billy explain the impact of his gangland reign upon the square.

In November, Johnny noticed that the CCTV system at Scarlet had recorded a conversation between Den's widow, Chrissie (Tracy-Ann Oberman), and Jake himself.

As Grant and Billy work with Peggy to get Sam exonerated, Phil begins a conflict with Johnny, as he continues to warn him to stay away from his mother.

While Phil and Grant work together to prevent Ian from buying the pub, Sam is released when the police catch up with Chrissie and arrest her for murdering Den — thus undoing Johnny's plan altogether.

In December, Johnny continues to clash with Phil and later becomes with his love rival Dennis Rickman (Nigel Harman) — who is Den's illegitimate son and married to his adopted daughter Sharon (Letitia Dean).

This escalates when Phil pays local waiter Juley Smith (Joseph Kpobie) to have a relationship with Ruby and then dump her, much to Johnny's annoyance.

However, Sharon objects to this and tells Phil that Johnny killed Andy in a bid to explain just how dangerous he is — pleading with him to let her and Dennis leave Walford.

However, Danny refuses to leave the mansion and even ignores Jake when his brother reminds him about the time Johnny originally planned to kill them both.

After learning from Ruby that it is the second anniversary of when her mother and sister were killed, Johnny obliges and is arrested; he is later sentenced to life imprisonment after confessing to all of his crimes, including the murders of Andy and Dennis.

In October, Johnny is contacted by Jake — who shares his concerns with him about Ruby's new relationship with Stacey's hothead brother Sean (Robert Kazinsky).

[1] The character made his debut appearance on 4 January 2005 and it was later revealed via Digital Spy that his daughter Ruby Allen (Louisa Lytton) and girlfriend Tina Stewart (Charlotte Avery) were also set to join the show.

The storyline focuses on Johnny after he retires from his life of crime and reunites the Mitchell brothers, Phil (Steve McFadden) and Grant (Ross Kemp).

In 2020, Sara Wallis and Ian Hyland from The Daily Mirror placed Johnny 87th on their ranked list of the best EastEnders characters of all time, calling him the "East End gangster.