Jacob is a former army medic turned nurse, who is given a job at Holby City Hospital after he brings a patient into the Emergency Department (ED).

Jacob was given connections within the ED through fellow nurse Louise Tyler (Azuka Oforka) and consultant Elle Gardner (Jaye Griffiths).

The character has had an on-off relationship with Connie Beauchamp (Amanda Mealing), which became popular with viewers who gave them the portmanteau #Jonnie on social media.

For his portrayal of Jacob, Venn won the Favourite Male TV Personality accolade at the 2016 Screen Nation Film and Television Awards.

Critics have had a mixed response to the character, with Alison Graham of the Radio Times calling him "a cocky narcissist", while Elaine Reilly from What's on TV thought he had become "one of the foundations of the ED".

On 13 February 2015, the BBC Media Centre announced Charles Venn had joined the cast of Casualty as new nurse Jacob Masters.

"[1] Shortly after he was cast as Jacob, Venn's mother told him that he would be working alongside his cousin, Azuka Oforka (who plays Louise Tyler).

"[2] The character's first scenes saw him entering the Emergency Department (ED) of Holby City Hospital and demand treatment for his friend.

[5] One of the Jacob's early storylines saw him implement a "controversial" gun and gangs protocol in the ED, following the admittance of a teenager who has been shot.

[6] Knowing Jackson (Louis Chandler-Joseph) is a member of a gang, Jacob worries that the hospital could be the setting for a revenge attack.

[6] During the thirtieth series episode "Belief", Jacob is involved in a terrorist incident at the hospital and is shot by a police officer.

[12] As Jacob and Connie treat Flo for a leg injury, she tells them that she is meeting up with her love interest, who has flown over from Australia to take her back with him.

[14] Connie is forced to amputate the patient's arm to get him out, but she and Jacob start arguing again and they fall through the floor when the roof suddenly caves in.

[14] When asked by Elaine Reilly of What's on TV if the couple would reconcile, Mealing expressed her desire to see them back together, as it was obvious they still cared for one another.

[10] The former couple are driving to a conference, where Jacob is due to give a speech, when they are flagged down by another driver, who tells them a man is stuck in a storm drain.

Connie and Jacob are soon "getting hot and heavy" in her room, and Ellis (Inside Soap) wondered if they could make their relationship work this time.

Mealing told David Brown of Radio Times that the accident would impact Connie's relationship with Jacob, leaving it strained.

When Connie blames fellow consultant and Jacob's friend Elle Gardner for Grace's condition, it leads to the couple breaking up for a second time.

"[21] Elle realises that Blake has injured himself after stealing alcohol from a shop, and Jacob helps to calm things down between mother and son.

They made time to rehearse the reveal scene and Griffiths admitted that it was hard, saying "We tried to avoid Elle and Jacob having a Star Wars 'I am your father' moment, which was very tricky!

[26] In April 2018, a potential romance between Jacob and paramedic Sam Nicholls (Charlotte Salt) was teased in the show's annual spring trailer.

[27] A couple of months later, the storyline began with Jacob providing support to Sam, after she endures a "traumatic" incident that occurred during her shift.

[28] Venn told Sarah Ellis of Inside Soap that Jacob sees Sam as someone who is "strong, confident, and very self-assured".

[30] Further exploration of the character's background began in September 2018, upon the introduction of his mother Omo Masters, played by Ellen Thomas.

[31] Sophie Dainty of Digital Spy said Jacob has a "complicated past" and series producer Lucy Raffety commented that mother and son would not have "a happy family reunion".

[32] Omo becomes further distressed when the voices in her head grow louder, and Jacob and Elle soon find her standing in the middle of the ED, having pulled out her cannula.

"[15] For his portrayal of Jacob, Venn won the Favourite Male TV Personality accolade at the 2016 Screen Nation Film and Television Awards.

[36] Holly Wade, writing for the same publication, said "Senior Staff Nurse Jacob has ruffled feathers since he joined the ED a few weeks ago.

[2] She also thought that he would make a big impression on the ED, like Venn's EastEnders character Ray Dixon did on Albert Square.

[39] A Daily Mirror reporter branded Jacob "hunky", and they observed that he was "the hero of the Emergency Department" after correctly diagnosing two poisoned patients.