-William 'Tripp' Van Der Bilt III is a recurring character in the Gossip Girl TV series. He is introduced as Nate Archibald's older "political minded" cousin, who got married in the second season to Maureen Van Der Bilt. The events of his political campaign drive Tripp towards an affair with Serena van der Woodsen that does not bode well for his political career. Tripp Van Der Bilt is portrayed by Aaron Tveit.
Ambitious and focused, Maureen once told Vanessa that Tripp dreamed of being an archaeologist but his grandfather redirected his attention to politics. Vanessa sees Tripp's ambitious nature first hand when he convinces her that politics is an inevitable choice for a Vanderbilt and Nate would soon follow his grandfather. Tripp later becomes a congressman in the show's third season and eventually stands up to his grandfather when fake video of him saving a man from drowning nearly ended his political career. Although he is first introduced a morally upright person, his relationship with Serena sends him into a downward spiral where his marriage and his career both become compromised. His infatuation with Serena develops into a dangerous obsession and a car crash injuring them both has Nate realize how low he has descended as a person. Tripp placed Serena into the driver's seat to preserve his image and get Serena implicated into causing the car crash, showing that he is capable of selfish self-preservation.
With Vanessa's requests, Nate decides to confront his family during a reunion to patch things with them. Their arrival however takes a different turn for relationship. During a conversation with Maureen at the reunion, Vanessa discovers that Tripp originally wanted to be an archaeologist and that their grandfather, William Van Der Bilt persuaded him to take a career path in politics. Vanessa then fears that their family will take control of Nate's future when he changes his plans about returning to his family. Tripp and William slowly bring him back to the family fold, bringing further away from Vanessa. Nate eventually decides to take the internship at the New York City Mayor's office that Tripp previously offered him to take.
During a party at the Van Der Bilt compound, Tripp tells Vanessa about Nate's internship at the Mayor's office leaving Vanessa upset that Nate would choose the internship over their backpacking trip across Europe. Tripp unfortunately creates a strain in Nate and Vanessa's relationship. When William announces Nate's internship during a toast, Tripp witnesses Nate publicly accepting it.
The third season has Tripp running for a congress that recently opened when Nate told Serena that Congressman Krueger had died and Tripp planned to take congressional seat. During a poker game that would free Carter Baizen from the Buckleys, Nate has Serena playing poker and raises the stakes when the game turns for the worse. Nate offers a photo of Tripp holding a bong and smoking marijuana in exchange for Carter's freedom. Serena loses the game and the photo that could ruin Tripp's campaign but soon finds out that Nate used her so that the real photo of Tripp holding a drink instead of a bong could be revealed to outmaneuver the Buckleys when they attempt to sabotage Tripp's campaign using the fake photo of Tripp. Serena's discovery strains her relationship with Nate.
During the week of elections, Chuck hosts the Van Der BiltElection party at the Empire Hotel with Nate helping in the campaign and Vanessa filming the events of the campaign. Serena, still not forgiving Nate for betraying her, asks Tripp for help in entering the Van Der Bilt Election party to get her job underway.
While taking a walk with Nate along the Hudson River, the two spot a man drowning and Tripp dives in to save him. Vanessa films the scene and the rescue reaches the morning news. Nate however, is suspicious of the rescue and confronts his grandfather about the entire event. Vanessa shares the same suspicion when she uncovers the truth about the rescue when she edits her film. The drowning man jumped into the Hudson River on purpose so that Tripp could save him and the positive publicity would get him an edge on his campaign by getting a few more votes.
The truth about the rescue eventually comes out during the Van Der Bilt Election party with Tripp and Nate bringing both suspicions about the fake rescue to their grandfather and later accuse him. William states that he didn't concoct the drowning incident but Nate and Tripp refuse to accept his statement. Nate then takes the fall for his grandfather and Tripp by publicly stating that he set-up the fake rescue. Moments after Nate's speech, the media announces that Tripp won the election and Tripp happily embraces his wife. When Serena quits her publicist position with K.C. Cunningham, she later meets Tripp at the hotel bar and form a friendly connection.
Serena seeks out to find work and takes a job as an aide for Tripp and is hired on the spot. While working for him, Trip confesses that he has developed feelings for her and she leaves Tripp's office to continue hosting the Cotillion. Serena, still having a fight with Blair, gets stuck in an elevator with her as a part of Chuck's set-up for the two to fix their strained friendship. Serena confesses to having the same feelings as Tripp does for her but Blair reminds her that Tripp is a married congressman and that crossing that line would be dangerous. When the two fixed their friendship, Serena returns to Tripp's office and Tripp persuades her to stay. Blair sees the tension between Serena and Tripp and leaves.
Tripp tries to stay professional with Serena but later events would result in an affair. Tripp sets out to start an affair with Serena when he discovers that Maureen created the drowning incident that would win him the election. When Serena seeks Nate's help in avoiding Tripp, saying that she is afraid of developing a relationship with him, Serena and Nate go to a bar for drinks. While Nate falls for Serena he tells her about that night of the mascara ball and how he owed her and then they lean in for a kiss. Tripp sees Serena with Nate and tells her about Maureen's plotting. He persuades her to go with him and the two kiss at his office.
Their affair ruins his marriage when they are discovered during a disastrous Thanksgiving despite their efforts to keep the secret hidden. Nate shows a video of Tripp and Serena kissing inside an elevator to Maureen. Serena leaves with Tripp on their way to a country home outside of the city.
The following day, Tripp and Maureen agree to certain terms concerning Serena and his career. Serena refuses to agree to becoming a mistress while Maureen remains as Tripp's wife and Serena decides to leave Tripp. Tripp offers her a ride home and their relationship ends. While on the road back to Manhattan, Tripp and Serena collide towards a bridge and Tripp places Serena on the driver's seat to remove himself from any implication of arrest. Nate later punches him for getting Serena into an accident when Tripp asks if he could see her.