Stuart "Stu" St. John is the estranged husband of Lenore Mills. Initially a supporting character, he becomes the main antagonist in Taken 3.
Stuart seems nice enough, chatting with Bryan Mills briefly. However he does not say much and seems rather competitive and stuck-up, upstaging Bryan's gift of a karaoke machine with a horse. Bryan later arrives at his mansion after Kim is kidnapped, and demands a private plane from Stuart to Paris, asking him if he knows anyone who would want revenge on him, citing an oil deal with some Russians that went south in 2004.
Stuart declines, claiming that he has contacts of his own and Bryan angrily tells him that "now is not the time for dick measuring". Bryan then goes to France on Stuart's plane. Stuart later offers Bryan a ride after he saves Kim but Bryan declines, taking a cab instead.
Although Stuart does not appear in the second film, it is revealed he left Lenore in between the two movies.
He returns in Taken 3 as the film's primary antagonist, where his last name is revealed to be St. John. He is also given his biggest role in the franchise yet, although he is played by a different actor.
Lenore confides in Bryan that Stuart and her are having relationship issues, and that she has begun to rekindle her romantic feelings for Bryan, however Bryan refuses to allow himself the pleasure of Lenny's company until such a time as she and Stuart work out their problems. Aware of the relationship between Lenny and Bryan, Stuart comes by Bryan's apartment to ask him politely but firmly to stay away from Lenny. The following day, Lenore is brutally stabbed to death while Stuart is in Las Vegas, Nevada on business. Bryan is framed for the murder, but evades police pursuit. Bryan goes to a remote convenience store where Lenore visited a day prior. He recovers surveillance footage of Lenny being grabbed by unidentified men. Bryan slowly figures out that the killers are the very same Russians that he mentioned in the first film, whose corrupt business dealings went south yet again and now threaten their family.
On 6 June 2014, Bryan captures Stuart and tortures him through means of waterboarding to force him to admit to his role in all this. Stuart admits that Lenore was killed because her insurance policy could pay off the Russians and they could frame Bryan for the murder. Bryan orders Stuart to help him bring the perpetrators to justice or he will be killed. With no choice, and again being reminded of Kim's danger, Stuart agrees. With assistance from his CIA colleagues and a reluctant Stuart, Bryan learns of the lead Russian mobster, former Spetsnaz, Oleg Malankov.
Bryan gains entry into Molankov's heavily guarded suite and dispatches the heavily armed guards, which leads to a fierce battle between the two special operatives. Finally, Bryan ends up mortally wounding Molankov, whereupon he learns that Stuart had played both men against each other, knowing that Bryan would kill Molankov and hopefully die as well, thus eliminating all the loose ends, freeing his debt and leaving him with twelve million dollars. In a delivery truck in the garage below the suite, Kim learns that while visiting Bryan to tell him to stay away from Lenore, he had taken Bryan's phone and sent a text to Lenore, asking to meet him at the gas station where she would later be abducted. When Kim attempts to warn Bryan of the danger that Stuart poses to him, Stuart shoots and wounds Sam and abducts Kim, intending to flee the country with the 12 million dollars he collected in life insurance from Lenny's death.
Bryan, despite injuries he sustained in his earlier encounter in Molankov's suite, gives chase in a Porsche. After locating his daughter from the tracker in her phone Bryan arrives at the airport just as Stuart's plane begins preparations for take off. After disabling the plane with the car, Bryan confronts Stuart and engages in a brief but violent struggle with him. Ultimately, Bryan emerges victorious and elects not to kill Stuart, warning him that if he serves only a limited time in jail for Lenny's murder he will answer to Bryan for Lenny's death when he is released. Bryan remarks "I will look for you, I will find you, and we both know what's gonna happen" then Bryan Knocks him out brutally then Dotzler and his LAPD officers arrive shortly afterward and arrest a now terrified Stuart.