Karl Kennedy is a fictional character from the Australian soap opera Neighbours, played by Alan Fletcher. The actor previously appeared in the soap in 1987 as mechanic Greg Cooper. He made his first screen appearance as Karl during the episode broadcast on 20 September 1994. Karl and his family were created by Neighbours storyliners in an attempt to bring the show back to its roots. Karl was given the job of local GP to provide him with immediate links to other characters. Debuting shortly before his wife, Susan Kennedy (Jackie Woodburne), and appearing continuously since his introduction, he is the longest serving character in the series' history.

In 1994, the Neighbours' storyliners decided to introduce the "solid" Kennedy family. They felt that they needed to take the show back to its roots when it seemed that all the houses on Ramsay Street were populated with misfits and distant relatives. Karl's wife Susan Kennedy (Jackie Woodburne) was given the job of teacher at the local school and Karl was made the local GP, giving the family immediate links with other characters.

Alan Fletcher had previously starred in Neighbours as Greg Cooper for a three-week guest role in 1987. When the character of Karl Kennedy came up, Fletcher auditioned for the role in the same way as he had for the role of Greg. He was subsequently cast in the show again seven years after his first appearance. Fletcher was pleased when he learned that Woodburne would be playing his character's wife, as they previously worked together on Cop Shop. He commented that they "struck a chord with each other when we first worked together". Fletcher admitted that when he joined the show again he thought he would be there for a year. He stated "I started on a one-year contract and the producers said, 'Do you want to do another year,' and I thought, oh, that is nice. Then my mind started turning towards four years but they kept asking me back. I don't know why."

In 2009, Fletcher celebrated the 15th anniversary of his character's arrival on Ramsay Street. In 2013, Fletcher filmed his 4,500th episode. The following year, Fletcher celebrated 20 years on the show. He commented "I am planning to hang around for quite a while longer because I do love it too much, we're talking at the moment about a continuation." Of his longevity on the show, Fletcher explained that leaving for the US to find work would not have "suited" him or his family, who he said were his "focus the whole time I've been on Neighbours. He said he enjoyed the job too much and thought it would be "perverse" for him to leave something he loved.

Susan and Karl were childhood sweethearts who married in 1978, before they both graduated from university. Karl has cheated on Susan and the couple have broken up and divorced, but they later reunited and have remarried. Karl and Susan are best friends who enjoy each other's company, share a deep connection and take joy in each other's quirks and ways. Woodburne described them as having a "really solid foundation for a marriage" and she has said that she does not want to see Susan and Karl's relationship break up again.

A writer for Holy Soap has called Susan and Karl "contenders for the friskiest couple on Ramsay Street". Following their "passionate arguments", the couple enjoy making up together as they have a healthy attraction for each other. Fletcher says he and Woodburne find the scenes "funny". Fletcher said "Karl and Susan every now and again do go through a phase where they become slightly more amorous than in their tougher times and tougher storylines – suffice to say it's not bawdy, but I think the audience will enjoy the fun aspect". Karl and Susan have been caught in the nude together on three occasions; at the beach, in Lou Carpenter's (Tom Oliver) spa and when they went skinny-dipping in the bush.

Upon the news that Neighbours would be concluding on 28 July 2022, Fletcher said that the finale would be a "huge celebration of the show, but a celebration that goes back 37 years. It'll be quite memorable." He described Channel 5's decision to cancel the show a "harsh reality", but understood why the decision had been made. When asked of his favourite storyline, Fletcher said, "Well, it's hard to get past the Izzy/Karl/Susan triangle, because unlike the Sarah affair, which was very much an affair, the Izzy storyline was a lot more complex. Karl left Susan mentally for Izzy, before he left her physically. Izzy actually had no interest in Karl. It was only when Izzy found out she was pregnant with another man's child, and that man had died in the Lassiters fire, that she said: 'I'll take you Karl, so you can be the father to my child'. Of course, she faked the date of her pregnancy at the hospital. It was an incredible story. Susan's reaction to Karl having a baby with another woman was spectacular. She really gave it to me in the street. It had many twists and turns and finished beautifully."

Fletcher also stated that he enjoyed comedic storylines, especially the serial's 7000th episode, where Karl shares a nude lunch. Fletcher explained that his least favourite storyline as Karl was when "he got himself a job as a pharmaceutical rep. He discovered that the company that he was working for were selling expired medicines in third world countries", and he thought the storyline unrealistic for Neighbours. Fletcher added that he and Woodburne were "very excited" for Izzy and Malcolm's returns in the final episodes. Upon the idea of Karl and Susan leaving the street at the end of the serial, Fletcher responded, "For me to fulfil my fantasy that Karl and Susan go on holiday on the last episode and turn up over the next year in every UK soap as tourists – for that to happen, I guess we'd have to leave!"