Terry Sullivan is a fictional character from the British Channel 4 soap opera Brookside, played by Brian Regan. One of the show's original characters, Terry debuted on-screen during the episode broadcast on 17 November 1982. Regan appeared in the show between 1982 and 1997. At the time of his departure, Regan was Brookside's longest serving cast member. Terry became one of Brookside's most iconic characters and was recognisable via his trademark curly permed hair and moustache. Terry also became known as one of soap opera's most unlucky characters because of his numerous storylines involving trauma, loss and heart-break. Writers created an on-screen partnership between Terry and Barry Grant (Paul Usher). Their friendship is endured for their entire tenure. Their characterisation was the inspiration for the comedy sketches titled The Scousers, which appeared in the television show, Harry Enfield's Television Programme.

Terry is portrayed as unlucky in love as writers paired him in doomed relationships with Michelle Jones (Tracey Jay) and Vicki Cleary (Cheryl Leigh). His later relationship with Sue Harper (Annie Miles) became a prominent storyline. The pair marry after she becomes pregnant with a son, Danny (Keiran Poole). Sue deceives Terry into believing he is the child's father and later discovers the truth. Writers continued to destroy the Sullivan marriage by creating a sexual affair between Sue and Barry. Sue and Danny were killed off in a mystery "Whodunit" story to celebrate the show's 1000th episode. Producers kept the identity of Sue's killer a secret and included Terry in the official suspects. Barry was later revealed as the killer, which tested their lifelong friendship once Terry discovered the truth. Producers planned violent content for Terry and Barry's showdown after he discovers his friend's betrayal. The episode featuring Terry's violence was one of the show's most difficult to produce due to production blunders. It was also controversial and condemnation from the Independent Television Commission forced a reshoot and a mellowed reaction from Terry.

Brian Regan, a former footballer turned actor took on the role of Terry in 1982. Terry is one of the show's original characters and he debuted on-screen during the sixth episode broadcast on 17 November 1982. Terry was originally a recurring character but Regan was promoted to the show's regular cast the following year. Regan has stated that joining the cast of Brookside in his mid-twenties gave him the "cotton-wool feeling of security" like when he was at school.

When Terry was introduced, he was not living on Brookside Close and resided on the local housing estate. In early episodes, writers established a close friendship with Barry Grant (Paul Usher). In his book, Brookside: The Official Companion, show creator Phil Redmond wrote that Terry is characterised as a "scallywag" type. Writers often portrayed Terry as an unlucky-in-love character with numerous failed relationships. The author of Life in the Close, Geoff Tibballs assessed that Terry was "forever unlucky in love" and has "many business exploits". Regan believed that he and Terry had different personalities but shared some similarities. Regan told Caro Thompson from TVTimes that "in other ways I'm not like Terry at all. I think I'm much more aggressive than he is. He's so easy-going he's a pushover. Although underneath, he's quite strong and if he's pushed too far he'll snap."

Annie Miles, who plays Terry's later wife, Sue Sullivan described him as a "nice fella" with a "big heart". He treats women differently to early stereotypes of men who expect their dinner on the table in the evening by carrying out house chores. She also characterised Terry as a "scally" but more so "a loveable scally." Terry's "nice and kind" characterisation made him popular with female viewers. Regan recalled that a female viewers told him that she and her friendship group wished they could find a man like Terry. Regan enjoyed playing Terry more after realising the appeal of his genuine persona. Regan has stated that he disliked portraying Terry's "lovey-dovey" scenes because he was bashful and often got embarrassed with large crews around filming Terry's romantic scenes. Regan told Nick Fisher from TV Guide that Terry had transformed into a mature character via fatherhood. He thought that during Terry's early storylines, he had allowed himself to suffer and let women destroy his life. Regan wanted Terry to become more "gangster" and a "bastard" even though he retained his "soft spot" traits. Producers also explored Terry's character further with the introduction of his father, Jack Sullivan played by William Maxwell. He becomes known to take part in fraudulent activities and near criminal activity.

Terry's image is something that Regan himself developed. The character became known for his trademark moustache and curly hair, which Regan grew especially for Terry's on-screen image. He originally grew a moustache because he was told his faced looked "soft" and "girly". He believed it made the character appear more "macho". Regan added that if he stopped playing Terry, he would shave off his moustache. In 1986, Regan injured his ankle while watching a football match. His injury forced production to rewrite Terry's storylines and use other characters in scenes.

Writers created Terry's first relationship with Michelle Jones (Tracey Jay). Her sister, Marie Jackson (Anna Keaveney) takes a dislike to Terry. She dislikes Terry's friendship with Barry and believes he is only interested in Michelle's new found wealth following the death of their sister, Petra Taylor (Alexandra Pigg). Michelle is a trainee beautician and wants to better herself, she takes it upon herself to make Terry look more presentable.

Michelle's brother-in-law, George Jackson (Cliff Howells) is framed for a robbery he did not commit. Local gangster Tommy McArdle (Malcolm Tierney) and his associate Victor Scott (Robbie Dee) force Terry and Barry to provide them with an alibi. This creates issues for the couple but Terry cannot defy McArdle because he fears violent retaliation. Terry and Barry later try to help George by striking a deal with police to implicate McArdle, but George is imprisoned regardless. McArdle retaliates by having Terry and Barry attacked. Terry is beaten more severely and spends time in hospital on an intensive care unit.