Stuart "Stu" St. John was the estranged husband of Lenore Mills. Initially a supporting character, he became the main antagonist in Taken 3.
Stuart seemed nice enough, and chatted with Bryan Mills briefly. However he did not say much, seemed rather competitive and stuck-up, and upstaged Bryan's gift of a karaoke machine with a horse. Bryan later arrived at his mansion after Kim was kidnapped, and demanded a private plane from Stuart to Paris, asked him if he knew anyone who would want revenge on him, and cited an oil deal with some Russians that went south in 2004.
Stuart declined, and claimed that he had contacts of his own and Bryan angrily told him that "now is not the time for dick measuring". Bryan then went to Paris on Stuart's plane. Stuart later offered Bryan a ride after he saved Kim, but Bryan declined, and took a cab instead.
Although Stuart did not appear in Taken 2, it was revealed that he had left Lenore in between the two films.
Stuart returned in Taken 3 as the film's primary antagonist, where his last name was revealed to be St. John. He was also given his biggest role in the franchise, although he was played by a different actor.
Lenore confided in Bryan that Stuart and her had relationship issues, and that she had begun to rekindle her romantic feelings for Bryan, however, Bryan refused to allow himself the pleasure of Lenny's company until such a time as she and Stuart workd out their problems. Aware of the relationship between Lenny and Bryan, Stuart came by Bryan's apartment to ask him politely but firmly to stay away from Lenny. The following day, Lenore was brutally stabbed to death while Stuart was in Las Vegas on business. Bryan was framed for the murder, but evaded police pursuit. Bryan went to a remote convenience store where Lenore had visited the day prior. He recovered surveillance footage of Lenny being grabbed by unidentified men in a black van. Bryan slowly figured out that the killers were the very same Russians that he mentioned in Taken, whose corrupt business dealings went south again and threatened his family.
On June 6, 2014, Bryan captured Stuart and tortured him through means of waterboarding in order to force him to admit to his role in all that. Stuart admitted that Lenore was killed because her insurance policy could pay off the Russians and that they could frame Bryan for the murder. Bryan ordered Stuart to help him bring the perpetrators to justice or he would be killed. With no choice, and again being reminded of Kim's danger, Stuart agreed. With assistance from his CIA colleagues and a reluctant Stuart, Bryan learned of the lead Russian mobster, former Spetsnaz, Oleg Malankov.
Bryan gained entry into Molankov's heavily guarded suite and dispatched the heavily armed guards, which lead to a fierce battle between the two special operatives. Finally, Bryan ended up mortally wounding Molankov, whereupon he learned that Stuart had played both men against each other, knew that Bryan would kill Molankov and hopefully die as well, and thus eliminate all of the loose ends, freeing his debt and leaving him with twelve million dollars. In a delivery truck in the garage below the suite, Kim learned that while visiting Bryan to tell him to stay away from Lenore, Stuart had taken Bryan's phone and sent a text to Lenore, that asked to meet him at the gas station where she was later abducted. When Kim attempted to warn Bryan of the danger that Stuart posed to him, Stuart shot and wounded Sam, abducted Kim, and intended to flee the country with the 12 million dollars that he had collected in life insurance from Lenny's death.
Bryan, despite injuries that he had sustained in his earlier encounter in Molankov's Suite, gave chase in a Porsche. After he located Kim from the tracker in her cellphone, Bryan arrived at the airport just as Stuart's plane began to prepare for take off. After he disabled the plane with the car, Bryan confronted Stuart and engaged in a brief, but violent struggle with him. Ultimately, Bryan emerged victorious, elected not to kill Stuart, and warned him that if he served only a limited time in jail for Lenny's murder, he would answer to him for Lenny's death when he was released. Bryan remarked: "I will look for you, I will find you, and we both know what's gonna happen" then knocked Stuart out brutally. Franck Dotzler and the LAPD officers arrived shortly afterward and arrested a terrified Stuart.