The fashion, glitz, and glamor of Gossip Girl was a definite attraction for fans, but the villainy of every character kept the show going. It's safe to say that almost every single person on the Upper East Side had an evil side to them, but the bad guys like Carter Baizen, Juliet Sharp, and Georgina Sparks were the most fun to watch as they brought the wealthy to their knees.
Every villain on the show had their schemes, their flair, and their unique ways of going about destroying the lives of Blair, Serena, Chuck, Nate, and Dan. Many of them had arcs and plots which kept audiences hooked, while the others were just about average.
Gabriel Edwards
Poppy Lifton's initial partner-in-crime seemed to be a big bad at first, but his lack of control over the situation made him a disappointing charlatan in the end. After going through with most of Poppy's plan, he had a change of heart, but only after he had already sent Poppy all the stolen money.
His motives were unclear, as was his last declaration of love for Serena. It was weird of him to develop a conscience suddenly, after probably helping Poppy do her dirty work many times previously.
Russel Thorpe
Chuck's nemesis was a sinner as they come, but his personality was a bit of a damper on the bad things he had done and was capable of doing. Thorpe had locked his wife in a burning building to kill her for a mere affair, pinned the blame on Bart, and then raised his daughter without telling her the truth.
As an act of revenge, he also tried to burn Blair inside a building, but she was easily rescued by Chuck and the gang, and Russel got jail time for nearly two decades. Russel was knee-deep in awful stuff and crime, but he didn't have the style or charisma that a usual GG villain has.
Poppy Lifton
Serena's former best friend and socialite buddy Poppy was an unexpected villain, which surprised viewers in a good way. She seemed like a fluffy side character until her elaborate schemes to trap the rich and steal their investments in a "charitable cause" came to light, and her ability to con someone like Serena by using Gabriel.
She managed to exploit her weakness for men by sending him in as a long-lost acquaintance and then pulling off an elaborate breakup skit to make her trust Gabriel. The entire plan was not flawless but quite wily, and it seemed to have worked because, by season 6, Poppy was a designer.
Carter Baizen
Sebastian Stan's Carter Baizen was a memorable character who toed the line between good and bad too often to be a true scoundrel. He was well-loved by fans, and at the start of the show, he did many questionable things, like conning Nate out of millions, threatening him, and then helping the baddies at the gentlemen's club whisk away Chuck's love interest.
He even left Bree Buckley's cousin at the altar, but then strangely took a turn towards goodness. He helped Serena find her father, and even accepted punishment from the Buckleys, which struck him off his bad guy pedestal very quickly and unexpectedly.
Diana Payne
Many viewers are still confused about Diana's part in the whole Bass saga, and why she had to even bring in Chuck's mother at all, but she had pizzazz. The lady was a dynamite who came in, stole phones from the rich, scoped their secrets, and then aired their dirty laundry for them.
While bewildering, the entire sequence of events of the secret club, hiding Bart, and then working for Nate's grandfather was extremely intriguing to watch. She knew how to protect herself while smoothly wrecking others, which made her the classiest villain on the show.
Prince Louis
Blair and Louis were one of Gossip Girl, and with good reason. While Blair was not completely innocent, to pretend to be nice to her and love her long enough to make her wed him, just so that she would be trapped by a crushing dowry contract was another level of petty.
Louis knew how to play the long game and didn't take it lightly if someone disrespected him the way Blair did. He was twisted enough to show her a good time and then try to bankrupt her family for her errors, which made him a stone-cold killer to watch out for.
Juliet Sharp
An unpopular opinion about Serena has it that Juliet should have brought her down, and she almost did. One of the most focused and intelligent vamps of the show, Juliet's singular aim to avenge her brother made her very dangerous for the It Girl of the UES.
Her plan to alienate Serena from all her friends by using identical costumes, wear down her self-esteem by making her feel bad at Columbia, and drugging her to the point of no coming back was very cold and very disturbing, which made her lethal and a force to reckon with.
Bart Bass
The return of Bart Bass was one of the most unexpected events on Gossip Girl, but his sudden urge to destroy his son, make him look unhinged in the media, and then even kill him was just outrageous. Bart was always capable of awful things, but his mean streak in season 6 was unexpected and super-villainous.
The fact that the fates of Chuck and Blair hung in the balance because of him made Bart even more powerful, and his relentless attacks on Chuck and the audacity to fake his death made for some great baddie television.
Jack Bass
Jack may have helped Chuck and Blair right at the end of the show, but it doesn't erase how much he harassed Chuck through the show. He took particular joy in making his life miserable, even in the smallest ways like giving him a fake liquor license for his club.
This gleefully corrupt behavior wasn't always this innocent, as he was the man who had asked Chuck to trade Blair for his hotel, and forced himself on Lily when she took away Bass Industries from him. He got Chuck drugged and drunk, and then took him to a room full of Board , so Jack, while entertaining, was very scary too.
Georgina Sparks
One of the best parts of season 1 of Gossip Girl was Georgina's introduction because few characters could pull off being a villain in such a likable way. She roofied Serena's drinks, became Gossip Girl for months, tricked Dan into believing that Milo was his, and got people deported when she wanted.
Georgina was an expert at meddling and making things worse, or reaching specific people and inciting them to do her bidding. A little push from Sparks could make people do twisted things, and that's why she was such a great villain.